The is a

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

Kanagawa is a Prefectures of Japan, prefecture of Japan located in the Kantō region of Honshu. Kanagawa Prefecture is the List of Japanese prefectures by population, second-most populous prefecture of Japan at 9,221,129 (1 April 2022) and third-dens ...

and Yamanashi Prefectures on the island of

Honshū , historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island separa ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. The upper reaches of the river in Yamanashi prefecture are also sometimes known as the , and the portion near the river mouth as the . The river overall was sometimes referred to as the from the sweetfish (''ayu'') which were once abundant in its waters. The Sagami River drains

Lake Yamanaka is located in the village of Yamanakako in Yamanashi Prefecture near Mount Fuji, Japan. Lake Yamanaka is the largest of the Fuji Five Lakes in surface area and the highest in elevation. It is the third highest lake in Japan, with a mean surf ...

, the largest and easternmost of the

Fuji Five Lakes is the name of the area located at the base of Mount Fuji in the Yamanashi Prefecture of Japan. It has a population of about 100,000 and sits about above sea level. The name Fuji Five Lakes comes from the fact that there are five lakes formed by ...

in Yamanashi Prefecture. It loops northwest, then northeast through Yamanashi, before following a generally southerly course to exit into

Sagami Bay lies south of Kanagawa Prefecture in Honshu, central Japan, contained within the scope of the Miura Peninsula, in Kanagawa, to the east, the Izu Peninsula, in Shizuoka Prefecture, to the west, and the Shōnan coastline to the north, while the ...

of the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

between the cities of

Hiratsuka 260px, Hiratsuka City Hall is a city located in Kanagawa Prefecture, Japan. , the city had an estimated population of 257,316 and a population density of 3800 persons per km². The total area of the city is . Geography Hiratsuka is located in ...

and

Chigasaki is a Cities of Japan, city located in Kanagawa Prefecture, Japan. , the city had an estimated population of 242,798 and a population density of 6800 people per km². The total area of the city is . Geography The city is located on the eastern ba ...

. It is dammed at several locations along the way, forming a number of reservoir lakes, the largest of which are

Lake Sagami is an artificial lake located in Midori-ku, Sagamihara, Kanagawa in Japan's Kantō region. Created in 1947 after the Sagami River was dammed, it serves as use for recreational and hydroelectric purposes. The lake also served as venue for canoein ...

and

Lake Tsukui A lake is an area filled with water, localized in a Depression (geology), basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the World Ocean, oce ...

. The river has had to re-cut its course several times due to repeated eruptions of

Mount Fuji , or Fugaku, located on the island of Honshū, is the highest mountain in Japan, with a summit elevation of . It is the second-highest volcano located on an island in Asia (after Mount Kerinci on the island of Sumatra), and seventh-highest p ...

, and

river terrace Fluvial terraces are elongated terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a "tread", separated from either an adjacent floodplain, other fluvial te ...

s are in evidence along its upper reaches in Yamanashi. As the river crosses Kanagawa, it forms natural

levees A levee (), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually earthen and that often runs parallel to the course of a river in its floodplain or along low-lying coastlin ...

in the soft soils of the

alluvial plain An alluvial plain is a largely flat landform created by the deposition of sediment over a long period of time by one or more rivers coming from highland regions, from which alluvial soil forms. A floodplain is part of the process, being the sma ...

s of central Kanagawa's

Sagamino plateau The , also known as the or , is a wide plateau situated between the Tama Hills and the Sagami River in Kanagawa Prefecture, Japan. Near its northern boundary with the city of Sagamihara is a city in Kanagawa Prefecture, Japan. , the city h ...

, and forms almost no

river delta A river delta is a landform shaped like a triangle, created by deposition (geology), deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, res ...

as it exits into the ocean. The potential of the upper reaches of the Sagami River for

hydroelectric power Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and ...

development began to be developed in the 1930s, with the growth of industry and electrical consumption in the

Yokohama is the second-largest city in Japan by population and the most populous municipality of Japan. It is the capital city and the most populous city in Kanagawa Prefecture, with a 2020 population of 3.8 million. It lies on Tokyo Bay, south of To ...

industrial belt, and the growing need for a reliable supply of drinking and industrial water. Work on the

Sagami Dam The is a multi-purpose dam on the main stream Sagami River in Sagamihara, Kanagawa, Sagamihara, Kanagawa Prefecture on the island of Honshū, Japan. History The potential of the Sagami River valley for hydroelectric power development began to be ...

began in 1938; however, lack of funding and the advent of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

delayed completion until after the end of the war. In the post war period, the

Shiroyama Dam The is a multi-purpose dam on the main stream Sagami River in Sagamihara, Kanagawa Prefecture on the island of Honshū, Japan. History The potential of the Sagami River valley for hydroelectric power development began to be developed in the 1930s ...

was also completed on the main stream of the Sagami River in 1965. A number of dams have also been completed on the Nakatsu River, the main

tributary A tributary, or affluent, is a stream or river that flows into a larger stream or 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 drain the surrounding drainage ...

of the Sagami River, including the

Miyagase Dam The is a dam on the Nakatsu River, a main tributary of the Sagami River in Aikō District, Kanagawa Prefecture, Japan. It straddles the border between the village of Kiyokawa, town of Aikawa and the former town of Tsukui (now part of the cit ...

External links

Sagami River Science Museum, Sagamihara
(mouth) {{Authority control Rivers of Kanagawa Prefecture Rivers of Yamanashi Prefecture Rivers of Japan