A blackwater river is a type of

river A river is a natural flowing watercourse, usually freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the ...

with a slow-moving channel flowing through forested swamps or

wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...

s. As vegetation decays,

tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' (from Anglo-Norman ''tanner ...

s leach into the water, making a transparent, acidic water that is darkly stained, resembling black tea. Most major blackwater rivers are in the

Amazon Basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Boli ...

and the

Southern United States The Southern United States (sometimes Dixie, also referred to as the Southern States, the American South, the Southland, or simply the South) is a geographic and cultural region of the United States of America. It is between the Atlantic Ocean ...

. The term is used in fluvial studies,

geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...

geography Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, a ...

ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...

, and

biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditar ...

. Not all dark rivers are blackwater in that technical sense. Some rivers in temperate regions, which drain or flow through areas of dark black

loam Loam (in geology and soil science) is soil composed mostly of sand ( particle size > ), silt (particle size > ), and a smaller amount of clay (particle size < ). By weight, its mineral composition is about 40–40–20% concentration of sand–si ...

, are simply black due to the color of the soil; these rivers are ''black mud rivers''. There are also black mud

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environme ...

. Blackwater rivers are lower in nutrients than whitewater rivers and have ionic concentrations higher than rainwater. The unique conditions lead to flora and fauna that differ from both whitewater and clearwater rivers. The classification of Amazonian rivers into black, clear, and whitewater was first proposed by Alfred Russel Wallace in 1853 based on water colour, but the types were more clearly defined by chemistry and physics by from the 1950s to the 1980s. Although many Amazonian rivers fall clearly into one of these categories, others show a mix of characteristics and may vary depending on season and flood levels.

Comparison between white and black waters

Black and white waters differ significantly in their ionic composition, as shown in Table 1. Black waters are more acidic, resulting in an

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It h ...

concentration greater than that of the more neutral white waters. The major difference is the concentrations of

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...

, and

potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosp ...

; these are very low in black waters. This has ecological implications. Some animals need more calcium than is available in blackwaters, so for example,

snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class G ...

s, which need much calcium to build shells, are not abundant in blackwaters. The lack of dissolved ions in black waters results in a low conductivity, similar to that of rainwater. Black and white waters differ in their

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cr ...

ic fauna and flora. Tables 2 and 3 compare the number of planktonic animals caught in black and white water localities only a few meters apart. The black water was not as extreme an example as the Rio Negro system. However, it can be seen that the black water held greater numbers of

rotifer The rotifers (, from the Latin , "wheel", and , "bearing"), commonly called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John H ...

s but fewer

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...

s and

mite Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...

s. These crustaceans are important foods for larval fish. The zones where the two waters mix are attractive to ostracods and young fish. These mixing zones tend to have many animals. The abundance is shown in Table3, which compares animals in of water.

Comparison between clear and black waters

Blackwater rivers resemble clearwater rivers in having a low conductivity and relatively low levels of dissolved solids, but clearwater rivers have water that often only is somewhat acidic (typical pH ~6.5) and very clear with a greenish color. The main Amazonian clearwater rivers have their source in the Brazilian Plateau (such as Tapajós, Tocantins, Xingu and some right tributaries of the

Madeira ) , anthem = ( en, "Anthem of the Autonomous Region of Madeira") , song_type = Regional anthem , image_map=EU-Portugal_with_Madeira_circled.svg , map_alt=Location of Madeira , map_caption=Location of Madeira , subdivision_type=Sovereign st ...

), but some originate in the Guiana Shield (such as Nhamundá, Paru, and Araguari).

Blackwater rivers of the world

Amazonia

* Apaporis River: a tributary of the Japurá River * Arapiuns River: a tributary of the

Tapajós River The Tapajós ( pt, Rio Tapajós ) is a river in Brazil. It runs through the Amazon Rainforest and is a major tributary of the Amazon River. When combined with the Juruena River, the Tapajós is approximately long. It is one of the largest clear ...

* Coari River * Mazaruni River *

Mirití-Paraná River Mirití-Paraná is a town and municipality in the southern Colombian Department Department may refer to: * Departmentalization, division of a larger organization into parts with specific responsibility Government and military *Department (admi ...

Piorini River The Piorini River ( pt, Rio Piorini) is a river in Amazonas state in north-western Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. ...

* Potaro River: a tributary of the Mazaruni River * Rio Negro: The largest blackwater river in the world; one of the largest Amazonian tributaries. * Tahuayo River * Tefé River * Uatumã River * Urubu River * Vaupés River

Orinoco basin

* Morichal Largo River * Atabapo River: from the Guiana highlands of

Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in ...

west into the Orinoco * Caroní River: from the Guiana Highlands of Venezuela north into the Orinoco. * Caura River: from the Guiana Highlands of Venezuela north into the Orinoco *

Inírida River The Inírida (, Spanish: Río Inírida) is a river in the north-west of South America, in the territory of Colombia, the largest tributary of the Guaviare (the Orinoco River basin). The length of the river is , of which are navigable for small ...

: from Colombia northeast into the Guaviare River which flows into the Orinoco * Ventuari River: from eastern Venezuela southwest into the Orinoco * Vichada River: from Colombia east into the Orinoco * Tomo River: from Colombia east into the Orinoco * Tuparro River: from Colombia east into the Orinoco

Southern United States

* Ashepoo River: along with the

Edisto Edisto Island is one of South Carolina's Sea Islands, the larger part of which lies in Charleston County, with its southern tip in Colleton County. The town of Edisto Beach is in Colleton County, while the Charleston County part of the island is u ...

and the

Combahee River The Combahee River ( ) is a short blackwater river in the southern Lowcountry region of South Carolina formed at the confluence of the Salkehatchie and Little Salkehatchie rivers near the Islandton community of Colleton County, South Caroli ...

s in South Carolina makes up the

ACE Basin National Wildlife Refuge The Ernest F. Hollings ACE Basin National Wildlife Refuge is a portion of the larger ACE Basin area, and the only portions that are federally protected. The wildlife refuge is divided into two units: the Edisto River unit and the Combahee Ri ...

. * Big Cypress, Black Cypress, and Little Cypress and the small rivers in the watershed of Caddo Lake in

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

and

Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a U.S. state, state in the Deep South and South Central United States, South Central regions of the United States. It is the List of U.S. states and territories by area, 20th-smal ...

* Blackwater River: a tributary of the

Chowan River The Chowan River (cho-WAHHN)
, from the North Carolina Collection's website at the

Blackwater River: a major river in the western

Florida panhandle The Florida Panhandle (also West Florida and Northwest Florida) is the northwestern part of the U.S. state of Florida; it is a salient roughly long and wide, lying between Alabama on the north and the west, Georgia on the north, and the G ...

* Blackwater River, West Virginia: Located in the Blackwater Canyon in Tucker County. Blackwater Falls, a five-story waterfall, is located along this river with rapids ranging from ClassIII-V+. * Black River: a tributary of the Pee Dee River in

North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''no ...

and South Carolina *

Cape Fear River The Cape Fear River is a long blackwater river in east central North Carolina. It flows into the Atlantic Ocean near Cape Fear, from which it takes its name. The river is formed at the confluence of the Haw River and the Deep River (North Ca ...

, North Carolina: flows into the Atlantic Ocean. * Cashie River, North Carolina: flows into Albemarle Sound. * Caloosahatchee River,

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, a ...

: flows west from Lake Okeechobee to the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United S ...

. *

Chowan River The Chowan River (cho-WAHHN)
, from the North Carolina Collection's website at the

Albemarle Sound. *

Edisto River The Edisto River is one of the longest free-flowing blackwater rivers in North America, flowing over 250 meandering miles from its sources in Saluda and Edgefield counties, to its Atlantic Ocean mouth at Edisto Beach, South Carolina. It rises ...

, South Carolina: flows into the Atlantic Ocean. * Econlockhatchee River, a

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 drainag ...

of the St. Johns River in Central Florida. * Forked Deer River: located in West Tennessee * Four Hole Swamp, a tributary of the Edisto River in South Carolina. * Little Manatee River, Florida: flows into

Tampa Bay Tampa Bay is a large natural harbor and shallow estuary connected to the Gulf of Mexico on the west-central coast of Florida, comprising Hillsborough Bay, McKay Bay, Old Tampa Bay, Middle Tampa Bay, and Lower Tampa Bay. The largest freshwater ...

. * Great Coharie Creek, North Carolina: flows into the Black River. * Little Pee Dee River, South Carolina: flows into the Pee Dee River. *

Lynches River Lynches River, named for Thomas Lynch, Jr., signer of the Declaration of Independence, rises in North Carolina near Waxhaw, North Carolina, at about 700 feet (210 m) elevation, flowing only a short distance to the South Carolina border, and th ...

, South Carolina: flows into the Pee Dee River. *

Lumber Lumber is wood that has been processed into dimensional lumber, including beams and planks or boards, a stage in the process of wood production. Lumber is mainly used for construction framing, as well as finishing (floors, wall panels, w ...

/ Drowning Creek: located in North and South Carolina. Part of Lumber River State Park * Myakka River: 66 mile-long river with its headwaters in Manatee County, Florida. The Myakka River discharges into Charlotte Harbor. * Obion River: located in Northwest Tennessee * Ochlockonee River: a river in northern Florida * Ogeechee River: a 245-mile river in eastern

Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to t ...

that passes to the south of the city of

Savannah A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to ...

and enters the Atlantic Ocean at Ossabaw Sound. *

Ohoopee River The Ohoopee River is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed April 21, 2011 river in east-central Georgia in the United States. It is a tributary of the Altamaha River, w ...

: a 119-mile-long (192 km) river in east-central

. It is a tributary of the

Altamaha River The Altamaha River is a major river in the U.S. state of Georgia. It flows generally eastward for 137 miles (220 km) from its origin at the confluence of the Oconee River and Ocmulgee River towards the Atlantic Ocean, where it empti ...

, which flows to the Atlantic Ocean. * Pasquotank River: a river in Northeastern

North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia a ...

. Located between Camden and Pasquotank counties, the Pasquotank connects directly to the Albemarle Sound and is part of the Intracoastal Waterway via Elizabeth City. * Peace River: located in central Florida, flows into Charlotte Harbor. * Pithlachascotee River: a small river in central

* Pocomoke River: a river in southern

Delaware Delaware ( ) is a state in the Mid-Atlantic region of the United States, bordering Maryland to its south and west; Pennsylvania to its north; and New Jersey and the Atlantic Ocean to its east. The state takes its name from the adjacen ...

and southeastern

Maryland Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; ...

on the Delmarva Peninsula. The river is a tributary to the

Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the ...

. * Santa Fe River: a river in northern Florida * Satilla River: a river in southeast

that flows through the city of Waycross and empties into the Atlantic Ocean near Cumberland Island. * Scuppernong River: a small river in Washington and Tyrrell Counties in eastern

at Pettigrew State Park * Sopchoppy River: a river in northern Florida * St. Mary's River (Florida–Georgia): a 130-mile river located in southeast Georgia and is bordered by the Satilla River Basin to the north and the Suwannee River Basin to the west. * St. Johns River: The largest river in Florida. Flows north through Jacksonville and into the Atlantic. *

St. Sebastian River The Saint Sebastian River is a river in the U.S. state of Florida, a tributary of the Indian River west and north of the city of Sebastian. Dredging Dredging Dredging is the excavation of material from a water environment. Possible re ...

, Indian River County, Florida. * Suwannee River: a large river in southern

and northern Florida flowing into the Gulf of Mexico * Upper Little River, North Carolina: flows into the

. * Upper Nanticoke River, Delaware and Maryland: flows into the Chesapeake Bay. * Village Creek, a 63 Mile long stream in the Big Thicket region of southeast Texas: flows into the

Neches River The Neches River () begins in Van Zandt County west of Rhine Lake and flows for through the piney woods of east Texas, defining the boundaries of 14 counties on its way to its mouth on Sabine Lake near the Rainbow Bridge. Two major reservoirs, L ...

. * Waccamaw River, North and South Carolina: flows into the Atlantic Ocean. * White Oak River, North Carolina: flows into the Atlantic Ocean. * Wolf River: arises in Northern Mississippi and runs through southwest Tennessee/Memphis into Mississippi River

Northern United States

* Black River, New York: a river starting in the western Adirondacks that flows into

Lake Ontario Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north, west, and southwest by the Canadian province of Ontario, and on the south and east by the U.S. state of New York. The Canada–United States border sp ...

. * Black River (Gogebic County),

Michigan Michigan () is a U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest, upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the List of U.S. states and ...

: a river in the far western Upper Peninsula that flows into

Lake Superior Lake Superior in central North America is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. and the third-largest by volume, holding 10% of the world's surface fresh w ...

. The northern section of the river is listed as a National Wild and Scenic River. * Mullica River and its tributaries from the

Pine Barrens Pine barrens, pine plains, sand plains, or pineland areas occur throughout the U.S. from Florida to Maine (see Atlantic coastal pine barrens) as well as the Midwest, West, and Canada and parts of Eurasia. Perhaps the most well known pine-barre ...

New Jersey New Jersey is a U.S. state, state in the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. It is bordered on the north and east by the state of New York (state), New York; on the ea ...

, where the dark water is called cedar water *

Gooseberry River Gooseberry River is a 23-mile stream in Lake County, Minnesota, USA, draining into Lake Superior. It is known for its waterfalls, near its mouth in Gooseberry Falls State Park. The Gooseberry, like many of its neighboring streams, has an irregula ...

: a river in northern Minnesota that leaches from peat bogs and pine forests *

Ocqueoc River The Ocqueoc River ( ') is stream in Presque Isle County in the northeastern part of the lower peninsula in the U.S. state of Michigan. It is longU.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map acc ...

, Michigan: a river in the northern Lower Peninsula that flows in

Lake Huron Lake Huron ( ) is one of the five Great Lakes of North America. Hydrologically, it comprises the easterly portion of Lake Michigan–Huron, having the same surface elevation as Lake Michigan, to which it is connected by the , Straits of Ma ...

* Tahquamenon River,

: a river in the Upper Peninsula that flows into

* Tuckahoe River,

: a short river in southern New Jersey that flows into

Great Egg Harbor Great Egg Harbor Bay (or Great Egg Harbor) is a bay between Atlantic and Cape May counties along the southern New Jersey coast. The name derives from Dutch explorer Cornelius Jacobsen May's description of the plentiful birds laying eggs, naming th ...

Africa

* Most

Congo Congo or The Congo may refer to either of two countries that border the Congo River in central Africa: * Democratic Republic of the Congo, the larger country to the southeast, capital Kinshasa, formerly known as Zaire, sometimes referred to a ...

and Lower Guinean rivers that flow through rainforests are blackwater. * The Congo basin lakes Mai-Ndombe and Tumba are blackwater. * The New Calabar and Sombreiro Rivers (both exiting in the Niger River Delta) are blackwater.

Australia

* Gordon River,

Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...

: a river rising in the center of the island and flowing westward, emptying into Macquarie Harbour on the West Coast * Pieman River, Tasmania: a river on the West Coast which leaches from rainforests and heathlands * Davey River, Tasmania: a relatively small river in the southwest corner of the island which runs through extensive heathlands, peat bogs and button grass plains * Noosa River,

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...

: a small section of the Noosa River running between Lake Cootharaba and Lake Cooroibah Other rivers in Australia may experience infrequent 'blackwater events' associated with flood waters connecting to forested floodplains and these events may be associated with hypoxic waters ow oxygen Examples include the

Murray River The Murray River (in South Australia: River Murray) ( Ngarrindjeri: ''Millewa'', Yorta Yorta: ''Tongala'') is a river in Southeastern Australia. It is Australia's longest river at extent. Its tributaries include five of the next six longe ...

, Edward River, Wakool River and Murrumbidgee River.

Indonesia

Sabangau River Sabangau National Park (sometimes spelled Sebangau) is a national park in Central Kalimantan, a province of Indonesia in Kalimantan, the Indonesian part of the island of Borneo established in 2004. Between 1980 and 1995 the site was a massive l ...

Images of blackwater rivers

Amazon blackwater.JPG, Amazon tributary classified as blackwater Bald Cypress.JPG, Cluster of bald cypress trees in Trap Pond State Park in Southern

Manaus-Amazon-NASA.jpg, Manaus, the largest city on the Amazon River, from a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedi ...

satellite image, surrounded by the muddy Amazon river and the blackwater Rio Negro File:Blackwater and muddy water, Big Thicket NP. Jack Gore Baygall Unit, Hardin Co. TX; 3 Apr 2020.jpg, A cypress slough where baygall blackwater (left) mixes with the more typical muddy waters (right) of the region. Big Thicket National Preserve, Jack Gore Baygall Unit, Hardin Co. Texas; 3 April 2020 File:Caño Ceima Cachivera, Mitú, Vaupés.jpg, Caño Ceima Cachivera, Mitú, Vaupés: one of the most visited waterfalls and indigenous communities In Mitú, Colombia

References

{{Wetlands Aquatic ecology Rivers