Cook Inlet (;
Sugpiaq: ''Cungaaciq'') stretches from the
Gulf of Alaska
The Gulf of Alaska ( Tlingit: ''Yéil T'ooch’'') is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the ...
to
Anchorage
Anchorage, officially the Municipality of Anchorage, is the most populous city in the U.S. state of Alaska. With a population of 291,247 at the 2020 census, it contains nearly 40 percent of the state's population. The Anchorage metropolita ...
in south-central
Alaska
Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...
. Cook Inlet branches into the
Knik Arm and
Turnagain Arm
Turnagain Arm (Denaʼina language, Dena'ina: ''Tutl'uh'') is a waterway into the northwestern part of the Gulf of Alaska. It is one of two narrow branches at the north end of Cook Inlet, the other being Knik Arm. Turnagain is subject to climate e ...
at its northern end, almost surrounding Anchorage. On its southern end, it merges with
Shelikof Strait, Stevenson Entrance, Kennedy Entrance and Chugach Passage.
The Cook Inlet and both its arms are bodies of
brackish water
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuary ...
, containing a
turbid
Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of both water clarity and wate ...
mix of ocean salt-water and freshwater runoff from the various rivers and streams. The narrow channel of the inlet funnels the tides creating very fast-moving currents,
rip tide
A rip tide, or riptide, is a strong offshore current that is caused by the tide pulling water through an inlet along a barrier beach, at a lagoon or inland marina where tide water flows steadily out to sea during ebb tide. It is a strong tidal f ...
s, and occasional
bore tides.
Cook Inlet watershed is the most populated watershed in Alaska. The
watershed covers about of southern Alaska, east of the
Aleutian Range
The Aleutian Range is a major mountain range located in southwest Alaska. It extends from Chakachamna Lake (80 miles/130 km southwest of Anchorage) to Unimak Island, which is at the tip of the Alaska Peninsula. It includes all of the mountain ...
, south and east of the
Alaska Range
The Alaska Range is a relatively narrow, mountain range in the Southcentral Alaska, southcentral region of the U.S. state of Alaska, from Lake Clark at its southwest endSources differ as to the exact delineation of the Alaska Range. ThBoard on G ...
, receiving water from its
tributaries
A tributary, or an ''affluent'', is a stream or river that flows into a larger stream ('' main stem'' or ''"parent"''), river, or a lake. A tributary does not flow directly into a sea or ocean. Tributaries, and the main stem river into which the ...
, which include the
Knik River, the
Little Susitna River, the
Susitna and
Matanuska river
A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...
s,
Eagle River,
Ship Creek,
Resurrection Creek, Portage Creek,
Kenai River, and many others. The watershed includes the drainage areas of Mt.Denali and is the collection point for the runoff from many surrounding glaciers, leading to the high turbidity and large silt deposits. Within the watershed there are several
national park
A national park is a nature park designated for conservation (ethic), conservation purposes because of unparalleled national natural, historic, or cultural significance. It is an area of natural, semi-natural, or developed land that is protecte ...
s and the active volcano
Mount Redoubt, along with three other historically active
volcano
A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most oft ...
es. Cook Inlet provides navigable access to the
port
A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Hamburg, Manch ...
of
Anchorage
Anchorage, officially the Municipality of Anchorage, is the most populous city in the U.S. state of Alaska. With a population of 291,247 at the 2020 census, it contains nearly 40 percent of the state's population. The Anchorage metropolita ...
at the northern end, and to the smaller
Homer
Homer (; , ; possibly born ) was an Ancient Greece, Ancient Greek poet who is credited as the author of the ''Iliad'' and the ''Odyssey'', two epic poems that are foundational works of ancient Greek literature. Despite doubts about his autho ...
port further south. Before the growth of Anchorage,
Knik was the destination for most marine traffic in upper Cook Inlet. Approximately 400,000 people live within the Cook Inlet watershed.
Geography

Cook inlet, along with the
Kenai Peninsula
The Kenai Peninsula ( Dena'ina: ''Yaghenen'') is a large peninsula jutting from the coast of Southcentral Alaska. The name Kenai (, ) is derived from the word "Kenaitze" or "Kenaitze Indian Tribe", the name of the Native Athabascan Alaskan tribe ...
, the
Kenai Mountains
The Kenai Mountains ( Dena'ina: ''Yaghanen Dghili'') are a mountain range in the U.S. state of Alaska. They extend northeast from the southern end of the Kenai Peninsula to the Chugach Mountains, and have an average elevation of 3,000 to 5,00 ...
, the
Chugach Mountains
The Chugach Mountains of southern Alaska are the northernmost of the several mountain ranges that make up the Pacific Coast Ranges of the western edge of North America. The range is about long and wide, and extends from the Knik and Turnag ...
, and
Kodiak Island
Kodiak Island (, ) is a large island on the south coast of the U.S. state of Alaska, separated from the Alaska mainland by the Shelikof Strait. The largest island in the Kodiak Archipelago, Kodiak Island is the second largest island in the Un ...
, formed approximately 65 million years ago, just after the extinction of the dinosaurs. Like most of Alaska's mountains, they consist mainly of
sedimentary rock
Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...
and
metamorphic rock
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, caus ...
that were deposited on the ocean floor during the
Cretaceous period
The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 77.1 million years, it is the ninth and longest geologi ...
. This area, where a corner of the
Pacific Plate subducts under the
North American Plate, uplifted the ocean floor and compressed it, causing the crust to thicken and
scrunch. Tectonic forces lifted the mountains and peninsula out of the water, forming a valley that was cut off from the ocean to the north and the west. The rest of Alaska's mountains were formed in the same manner, in cyclic events, and the mountain ranges become progressively older the further north they lie. Thus, the Cook Inlet and its surrounding land masses are rather young compared to those of the
Alaska Range
The Alaska Range is a relatively narrow, mountain range in the Southcentral Alaska, southcentral region of the U.S. state of Alaska, from Lake Clark at its southwest endSources differ as to the exact delineation of the Alaska Range. ThBoard on G ...
, which formed around 126 million years ago, or the
Brooks Range
The Brooks Range (Gwich’in language, Gwich'in: ''Gwazhał'') is a mountain range in far northern North America stretching some from west to east across northern Alaska into Canada's Yukon Territory. Reaching a peak elevation of on Mount Isto, ...
which formed around 256 million years ago. The valley left by this continental compaction remains open to the
Gulf of Alaska
The Gulf of Alaska ( Tlingit: ''Yéil T'ooch’'') is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the ...
to the south, forming the inlet as it exists today. The surrounding mountains were host the large ice sheets and glaciers during the
Pleistocene epoch
The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
(the Ice Ages, around 2 million to 11,000 years ago) which scoured the land and formed vast plains and
moraine
A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...
s surrounding much of the upper inlet from
glacial till
image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...
that was deposited.
Cook Inlet exists in a
subsidence
Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...
zone which contains many
faults, and is frequently prone to
earthquake
An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...
activity. The primary fault, the Aleutian Fault, is found in the nearby
Aleutian Trench
The Aleutian Trench (or Aleutian Trough) is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench extends for from a triple junction in the west with the Ula ...
in the Gulf of Alaska, where a corner of the Pacific Plate is forced underneath Alaska at a 45-degree angle. Thus, most of the uplift force occurs along a line from Kodiak Island and up the Kenai Mountains to the Chugach mountains. The inlet lies in a region where the crust is wrinkled under this force and the tectonic forces push the ground downward. In 1964, the
1964 Alaska earthquake
The 1964 Alaska earthquake, also known as the Great Alaska earthquake and Good Friday earthquake, occurred at 5:36 PM Alaska Standard Time, AKST on Good Friday, March 27, 1964. , a
megathrust earthquake
Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthq ...
, occurred when over 600 miles of the Aleutian fault ruptured, uplifting the Kenai Mountains 60 feet (20 meters) in under 5 minutes. With a magnitude of 9.2, the earthquake was the fourth largest ever recorded. It devastated Anchorage where much of downtown dropped several stories, and the mountains surrounding the Turnagain Arm subsided 8 feet (2.4 meters), submerging the towns of
Portage
Portage or portaging ( CA: ; ) is the practice of carrying water craft or cargo over land, either around an obstacle in a river, or between two bodies of water. A path where items are regularly carried between bodies of water is also called a '' ...
and
Girdwood, as well as long stretches of the
Seward Highway
The Seward Highway is a highway in the U.S. state of Alaska that extends from Seward, Alaska, Seward to Anchorage, Alaska, Anchorage. It was completed in 1951 and runs through the scenic Kenai Peninsula, Chugach National Forest, Turnagain Arm ...
.

Because it lies along a
subduction zone
Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
, the Cook Inlet region contains active volcanoes, including
Augustine Volcano and
Mount Redoubt, and is part of the
Pacific Ring of Fire
The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a tectonic belt of volcanoes and earthquakes.
It is about long and up to about wide, and surrounds most of the Pa ...
. Hot magma and steam from the subducting ocean floor build up within these volcanoes, which tend to erupt in fairly regular cycles with very explosive force, often spewing volcanic ash tens of thousands of feet (several kilometers) high. Volcanic
eruption
A volcanic eruption occurs when material is expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has ...
s in the region have been associated with
earthquake
An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...
s and
tsunami
A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...
s, and debris
avalanche
An avalanche is a rapid flow of snow down a Grade (slope), slope, such as a hill or mountain. Avalanches can be triggered spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, othe ...
s have resulted in tsunamis also. There was an earthquake of the magnitude of 7.1 on December 31, 1901 generated by an eruption that caused several tsunamis. In 2009 a
lahar
A lahar (, from ) is a violent type of mudflow or debris flow composed of a slurry of Pyroclastic rock, pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a valley, river valley.
Lahars are o ...
from Mt. Redoubt threatened the
Drift River oil terminal.
Cook Inlet has the fourth largest tidal range in the world. The shape of the inlet and its orientation with respect to the lunar orbit causes the tide to come in and go out very rapidly. As the inlet narrows, the speed of the water increases, creating very powerful currents with speeds of up to 6 knots (7 miles per hour). While lined with large areas of silt and
mudflat
Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal ...
s, the central and upper inlet is filled with narrow troughs that may be 150 to 300 feet (50 to 100 meters) deep. These, along with the tides, provide a challenge to ships navigating through the waters. The strong tides create powerful rip tides and bore tides which are sometimes among the largest in the world.
Tidal bores
A tidal bore, often simply given as bore in context, is a tidal phenomenon in which the leading edge of the incoming tide forms a wave (or waves) of water that travels up a river or narrow bay, reversing the direction of the river or bay's cu ...
occur within the inlet, and especially Turnagain Arm, almost daily, but are usually too small to notice. Large bores tend to occur after extreme tidal lows, appearing as a wall of water sometimes over 10 feet high as the tide comes in all at once. Large bores are less frequent, and are typically formed during a new or full moon, especially when the moon is at
perigee
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values.
Apsides perta ...
. Unlike areas around the
Bering Sea
The Bering Sea ( , ; rus, Бе́рингово мо́ре, r=Béringovo móre, p=ˈbʲerʲɪnɡəvə ˈmorʲe) is a marginal sea of the Northern Pacific Ocean. It forms, along with the Bering Strait, the divide between the two largest landmasse ...
where weather is largely affected by sea ice, the waters of the inlet are warmed by the
Alaska Current
The Alaska Current is a southwestern shallow warm-water current alongside the west coast of the North American continent beginning at about 48-50°N. The Alaska Current produces large clockwise eddies at two sites: west of the Haida Gwaii (" Ha ...
in the Gulf of Alaska, part of the North-Pacific Subpolar
Gyre
In oceanography, a gyre () is any large system of ocean surface currents moving in a circular fashion driven by wind movements. Gyres are caused by the Coriolis effect; planetary vorticity, horizontal friction and vertical friction determine the ...
, which affects the climate and keeps the temperatures in the Cook Inlet region fairly moderate compared to the extremes found in other parts of the state.
History

The inlet was first explored and settled by
Alutiiq
The Alutiiq (pronounced in English; from Promyshlenniki Russian Алеутъ, "Aleut"; plural often "Alutiit"), also called by their ancestral name ( or ; plural often "Sugpiat"), as well as Pacific Eskimo or Pacific Yupik, are a Yupik ...
people, tribes of coastal-dwelling Pacific
Eskimo
''Eskimo'' () is a controversial Endonym and exonym, exonym that refers to two closely related Indigenous peoples: Inuit (including the Alaska Native Iñupiat, the Canadian Inuit, and the Greenlandic Inuit) and the Yupik peoples, Yupik (or Sibe ...
s, beginning around 6000 years ago. The
Chugach arrived around the first century and were the last of the Alutiiq people to settle in the area, but abandoned it after tribes of
Dena'ina people, an
Athabaskan
Athabaskan ( ; also spelled ''Athabascan'', ''Athapaskan'' or ''Athapascan'', and also known as Dene) is a large branch of the Na-Dene language family of North America, located in western North America in three areal language groups: Northern, ...
people from the interior of the state, arrived sometime between 500 and 1600 AD. In the 18th century, Russian fur hunters ''(
promyshlenniki)'' were among the first European visitors. The Lebedev Lastochkin Company leader Stepan Zaikov established a post at the mouth of the Kenai River,
Fort Nikolaevskaia, in 1786. These fur trappers used Siberian Native and Alaska Native people, particularly
Aleuts
Aleuts ( ; (west) or (east) ) are the Indigenous people of the Aleutian Islands, which are located between the North Pacific Ocean and the Bering Sea. Both the Aleuts and the islands are politically divided between the US state of Alaska ...
from the
Aleutian Islands
The Aleutian Islands ( ; ; , "land of the Aleuts"; possibly from the Chukchi language, Chukchi ''aliat'', or "island")—also called the Aleut Islands, Aleutic Islands, or, before Alaska Purchase, 1867, the Catherine Archipelago—are a chain ...
and Koniag natives from
Kodiak, to hunt for
sea otter
The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern Pacific Ocean, North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of ...
s and other marine mammal species for trade with
China
China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
via Russia's then-exclusive inland port of trade at
Kiakhta.
Other Europeans to visit Cook Inlet include the 1778 expedition of
James Cook
Captain (Royal Navy), Captain James Cook (7 November 1728 – 14 February 1779) was a British Royal Navy officer, explorer, and cartographer famous for his three voyages of exploration to the Pacific and Southern Oceans, conducted between 176 ...
, its namesake, who sailed into it while searching for the
Northwest Passage
The Northwest Passage (NWP) is the sea lane between the Atlantic and Pacific oceans through the Arctic Ocean, near the northern coast of North America via waterways through the Arctic Archipelago of Canada. The eastern route along the Arctic ...
. Cook received maps of Alaska, the Aleutians, and Kamchatka during a visit with Russian fur trader
Gerasim Izmailov in
Unalaska, and combined these maps with those of his expedition to create the first
Mercator projection of the North Pacific. The inlet was named after Cook in 1794 by
George Vancouver
Captain (Royal Navy), Captain George Vancouver (; 22 June 1757 – 10 May 1798) was a Royal Navy officer and explorer best known for leading the Vancouver Expedition, which explored and charted North America's northwestern West Coast of the Uni ...
, who had served under Cook in 1778.
Turnagain Arm
Turnagain Arm (Denaʼina language, Dena'ina: ''Tutl'uh'') is a waterway into the northwestern part of the Gulf of Alaska. It is one of two narrow branches at the north end of Cook Inlet, the other being Knik Arm. Turnagain is subject to climate e ...
was named by Cook, "turnagain" being a moniker he had used before, at his annoyance at having to turn around after exploring another dead end.
Upon reaching the head of Cook Inlet, Cook was of the opinion that both Knik Arm and Turnagain Arm were the mouths of rivers and not the opening to the Northwest Passage. Under orders by the
British Crown
The Crown is a political concept used in Commonwealth realms. Depending on the context used, it generally refers to the entirety of the State (polity), state (or in federal realms, the relevant level of government in that state), the executive ...
to ignore any such rivers and inlets, he had initially planned to pass it by, but at the insistence of
John Gore and many others of his crew, he reluctantly agreed to explore the area. Cook anchored at
Ship Creek and encountered the local Natives for the first time when two men approached in kayaks, invited them to come ashore. Under Cook's orders,
William Bligh
William Bligh (9 September 1754 – 7 December 1817) was a Vice-admiral (Royal Navy), Royal Navy vice-admiral and colonial administrator who served as the governor of New South Wales from 1806 to 1808. He is best known for his role in the Muti ...
, of fame, organized a party to travel up Knik Arm. Bligh served as Cook's Sailing Master on this, his 3rd and final voyage, the aim of which was discovery of the
Northwest Passage
The Northwest Passage (NWP) is the sea lane between the Atlantic and Pacific oceans through the Arctic Ocean, near the northern coast of North America via waterways through the Arctic Archipelago of Canada. The eastern route along the Arctic ...
. After meeting with some local Dena'ina, Bligh returned to report Knik Arm indeed led only to a couple of rivers.
Cook sailed up Turnagain Arm in his ship, , finding it impossible to navigate against the strong currents and mudflats, and got stuck on a sandbar when he tried to get back out, having to wait for the tide to come in and free his ship. He never actually confirmed it led to a river, which led to a decade of massive speculation until George Vancouver returned to finish the map. Having been in a bad mood since first agreeing to explore the area, and as a result of this frustration, the second body of water was given the disingenuous name "Turn Again". Early maps label Turnagain Arm as the "Turnagain River".

The SS ''Farallon'' was a wooden Alaskan Steamship Company liner that
struck Struck is a surname. Notable people with the surname include:
*Adolf Struck
Adolf Hermann Struck (1877–1911) was a German sightseer and writer. He is known for his Travel literature, travelogue ''Makedonische Fahrten'' and for surveying the ...
Black Reef in the Cook Inlet on January 5, 1910. All thirty-eight men on board survived, and were rescued twenty-nine days later. Few white people visited upper Cook Inlet until construction of the
Alaska Railroad
The Alaska Railroad is a Class II railroad that operates freight and passenger trains in the state of Alaska. The railroad's mainline runs between Seward, Alaska, Seward on the southern coast and Fairbanks, Alaska, Fairbanks, near the center of ...
along the eastern shores of Turnagain Arm and Knik Arm of Cook Inlet around 1915. The natives of the
Eklutna village are the descendants of the residents of eight native villages around upper Cook Inlet.
During the
1964 Alaska earthquake
The 1964 Alaska earthquake, also known as the Great Alaska earthquake and Good Friday earthquake, occurred at 5:36 PM Alaska Standard Time, AKST on Good Friday, March 27, 1964. , areas around the head of Turnagain Arm near
Girdwood and Portage dropped as much as by subsidence and subsequent tidal action. Both hamlets were destroyed. Girdwood was later relocated inland and Portage was abandoned. About of the
Seward Highway
The Seward Highway is a highway in the U.S. state of Alaska that extends from Seward, Alaska, Seward to Anchorage, Alaska, Anchorage. It was completed in 1951 and runs through the scenic Kenai Peninsula, Chugach National Forest, Turnagain Arm ...
sank below the high-water mark of Turnagain Arm; the highway and its bridges were raised and rebuilt in 1964–66.
Communities
Most of Alaska's population is in the Cook Inlet area, with highest concentration in
Anchorage
Anchorage, officially the Municipality of Anchorage, is the most populous city in the U.S. state of Alaska. With a population of 291,247 at the 2020 census, it contains nearly 40 percent of the state's population. The Anchorage metropolita ...
. Along the East side of the Cook Inlet, the
Kenai Peninsula
The Kenai Peninsula ( Dena'ina: ''Yaghenen'') is a large peninsula jutting from the coast of Southcentral Alaska. The name Kenai (, ) is derived from the word "Kenaitze" or "Kenaitze Indian Tribe", the name of the Native Athabascan Alaskan tribe ...
is host to many smaller fishing communities, such as
Kenai,
Soldotna, Ninilchick, Anchor Point and
Homer
Homer (; , ; possibly born ) was an Ancient Greece, Ancient Greek poet who is credited as the author of the ''Iliad'' and the ''Odyssey'', two epic poems that are foundational works of ancient Greek literature. Despite doubts about his autho ...
. Many residents of the Kenai rely on income generated from fisheries in the Cook Inlet. The west side of the Inlet is not connected to any major road systems and is typically accessed by boat or plane, including the village of
Tyonek, Alaska, some oil camps, and many seasonal fishing camps.
Resources
The Cook Inlet Basin contains large oil and gas deposits including several offshore fields. As of 2005 there were 16 platforms in Cook Inlet, the oldest of which is the ''XTO A'' platform first installed by
Shell
Shell may refer to:
Architecture and design
* Shell (structure), a thin structure
** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses
Science Biology
* Seashell, a hard outer layer of a marine ani ...
in 1964, and newest of which is the ''Osprey'' platform installed by Forest Oil in 2000. Most of the platforms are operated by Union Oil, which was acquired by Chevron in 2005. There are also numerous oil and gas pipelines running around and under the Cook Inlet. The main destinations of the gas pipelines are to Kenai where the gas is primarily used to fuel commercial fertilizer production and a liquified natural gas (LNG) plant and to Anchorage where the gas is consumed largely for domestic uses.
Alaska has approximately half the known coal reserves in the U.S. For decades, there has been a proposal to build a large coal mine (the
Chuitna Coal Mine) on the west side of Cook Inlet near the
Chuitna River, and the native village of
Tyonek, Alaska.
American Rivers
American Rivers is a nonprofit environmental advocacy organization focused on protecting and promoting the health of rivers in the United States. Established in 1973, the group is headquartered in Washington, D.C.
Activities River restoration
A ...
placed the
Chuitna River on its list of
America's Ten Most Endangered Rivers of 2007, based on the threat of this mine.

Turnagain Arm is one of only about 60 bodies of water worldwide to exhibit a
tidal bore
A tidal bore, often simply given as bore in context, is a tidal phenomenon in which the leading edge of the incoming tide forms a wave (or waves) of water that travels up a river or narrow bay, reversing the direction of the river or bay's cu ...
. The bore may be more than high and travel at on high
spring tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another.
Tide tables ...
s and opposing winds. Turnagain Arm sees the largest
tidal range
Tidal range is the difference in height between high tide and low tide. Tides are the rise and fall of sea levels caused by gravitational forces exerted by the Moon and Sun, by Earth's rotation and by centrifugal force caused by Earth's prog ...
in United States, with a mean of , and the fourth highest in the world, behind
Bay of Fundy
The Bay of Fundy () is a bay between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine. It is an arm of the Gulf of Maine. Its tidal range is the highest in the world.
The bay was ...
(),
Ungava Bay (), and
Bristol Channel
The Bristol Channel (, literal translation: "Severn Sea") is a major inlet in the island of Great Britain, separating South Wales (from Pembrokeshire to the Vale of Glamorgan) and South West England (from Devon to North Somerset). It extends ...
(). The ocean's natural 12-hour 25-minute tidal cycle is close to Turnagain Arm's natural resonance frequency, which then reinforces the tide similar to water sloshing in a bathtub. Tidal fluctuations in the main body of Cook Inlet, while not as extreme as the shallow and narrow Turnagain Arm, regularly reach or more and exhibit currents in excess of at full tidal flow. The inlet and its arms have been proposed as a potentially attractive site for the generation of
tidal power
Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods.
Although not yet widely used, tidal energy has the potential for future electricity generation. T ...
.
Turnagain Arm and Knik Arm are known for large areas of
silt
Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...
. At low tide, much of this is exposed, making marine navigation difficult. Historically, ships and boats designed for the area had a relatively flat bottom with a modest centerboard and absence of a large keel because the boats would occasionally become beached at low tide either on purpose or by accident. This design allowed the craft to support its weight on land without sustaining any serious damage to its structure. An example of this design is the Nomad, a much photographed fishing boat once owned by Joe Reddington which has sat on a mudflat near Knik for several decades.
These
mudflat
Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal ...
s can also be dangerous to walk on, exhibiting
quicksand
Quicksand (also known as sinking sand) is a colloid consisting of fine granular material (such as sand, silt or clay) and water. It forms in saturated loose sand when the sand is suddenly agitated. When water in the sand cannot escape, it crea ...
-like characteristics, and have claimed the life of at least four people who have wandered out on them, usually tourists, with many more being rescued every year.
Cruise ship
Cruise ships are large passenger ships used mainly for vacationing. Unlike ocean liners, which are used for transport, cruise ships typically embark on round-trip voyages to various ports of call, where passengers may go on Tourism, tours k ...
s dock at
Seward on the
Gulf of Alaska
The Gulf of Alaska ( Tlingit: ''Yéil T'ooch’'') is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the ...
or
Whittier in
Prince William Sound
Prince William Sound ( Sugpiaq: ''Suungaaciq'') is a sound off the Gulf of Alaska on the south coast of the U.S. state of Alaska. It is located on the east side of the Kenai Peninsula. Its largest port is Valdez, at the southern terminus of the ...
and transport passengers via bus or train to Anchorage. However, over 95% of freight entering Alaska comes through the
Port of Anchorage, which is served by major
container ship
A container ship (also called boxship or spelled containership) is a cargo ship that carries all of its load in truck-size intermodal containers, in a technique called containerization. Container ships are a common means of commercial intermodal ...
companies and other carriers.
Conservation

The Cook Inlet
beluga whale is a genetically distinct and geographically isolated stock. The population fell to 278 in 2005 and it is listed as
critically endangered
An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...
in the
IUCN Red List
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...
of Threatened Species. This was perhaps due to local hunt, although an article in the ''
Anchorage Daily News
The ''Anchorage Daily News'' is a daily newspaper published by the Binkley Co., and based in Anchorage, Alaska. It is the most widely read newspaper and news website (adn.com) in the state of Alaska. The newspaper is headquartered in Anchorage, ...
'' questioned this conclusion.
Killer whale
The orca (''Orcinus orca''), or killer whale, is a toothed whale and the largest member of the oceanic dolphin family. The only extant species in the genus '' Orcinus'', it is recognizable by its black-and-white-patterned body. A cosmopolit ...
s commonly feed on belugas in the Cook Inlet, driving them to the upper part of the inlet where they often seek refuge in the shallower waters of the arms.
In 2000, the US
National Marine Fisheries Service
The National Marine Fisheries Service (NMFS), informally known as NOAA Fisheries, is a United States federal agency within the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) that is responsible for the ste ...
listed the Cook Inlet beluga whale population as depleted and began development of a conservation plan. On October 22, 2008 the Cook Inlet beluga whale was put onto the endangered species list. Cook Inlet activities include commercial fishing, oil and gas development,
release of treated sewage, noise from aircraft and ships, shipping traffic, and tourism. However, it is not known what impact these activities had on the beluga whale population.
The Coastal Marine Institute at the
University of Alaska Fairbanks
The University of Alaska Fairbanks (UAF or Alaska) is a public university, public Land-grant university, land-, National Sea Grant College Program, sea-, and National Space Grant College and Fellowship Program, space-grant research university in ...
's School of Fisheries and Ocean Sciences working with the U.S. Department of the Interior's Minerals Management Service (MMS), began a three-year project in 2003 focusing on the water circulation in Cook Inlet.
Cook Inletkeeper, a member of the
Waterkeeper Alliance, began in 1994 when a group of Alaskans became concerned about the rapid ecological changes in the inlet. The group formally incorporated the following year using settlement proceeds from a Clean Water Act lawsuit against Cook Inlet oil and gas producers. Their stated mission is to "protect Alaska's Cook Inlet watershed and the life it sustains," with a focus on clean water, healthy habitat, local economies, and energy. They are based in
Homer
Homer (; , ; possibly born ) was an Ancient Greece, Ancient Greek poet who is credited as the author of the ''Iliad'' and the ''Odyssey'', two epic poems that are foundational works of ancient Greek literature. Despite doubts about his autho ...
.
See also

*
Alaska Wildlife Conservation Center
*
Augustine Volcano
*
Kalgin Island
*
Knik Arm Bridge
*
Lake Clark National Park
*
Captain Cook State Recreation Area
Notes
External links
United States, Alaska South Coast, Barren IslandsNational Ocean Service
The National Ocean Service (NOS) is an office within the U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA). It is responsible for preserving and enhancing the nation's coastal resources and ecosystems along appro ...
United States, Alaska South Coast, Cook Inlet, Anchor Point to Kalgin IslandNational Ocean Service
The National Ocean Service (NOS) is an office within the U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA). It is responsible for preserving and enhancing the nation's coastal resources and ecosystems along appro ...
Map of Cook Inlet oil and gas activity Alaska Department of Natural Resources
{{Authority control
Estuaries of Alaska
Bodies of water of Anchorage, Alaska
Bodies of water of Kenai Peninsula Borough, Alaska
Bodies of water of Matanuska-Susitna Borough, Alaska
Kenai Mountains-Turnagain Arm National Heritage Area
Monuments and memorials to James Cook