The longest rivers of the United States include 38 that have main stems of at least 500 miles (800km) long. The main stem is "the primary downstream segment of a river, as contrasted to its tributaries".[1] The United States Geological Survey (USGS) defines a main-stem segment by listing coordinates for its two end points, called the source and the mouth. Some well-known rivers like the Atchafalaya,[2]Willamette,[3] and Susquehanna[4] are not included in this list because their main stems are shorter than 500miles.
Seven rivers in this list cross or form international boundaries. Two—the Yukon and Columbia rivers—begin in Canada and flow into the United States. Three—the Milk and Saint Lawrence rivers and the Red River of the North—begin in the United States and flow into Canada. Of these, only the Milk River crosses the international border twice, leaving and then re-entering the United States.[5] Two rivers, the Colorado and the Rio Grande, begin in the United States and flow into or form a border with Mexico.[5] In addition, the drainage basins of the Mississippi and Missouri rivers extend into Canada,[6][7] and the basin of the Gila River extends into Mexico.[8]
Sources report hydrological quantities with varied precision. Biologist and author Ruth Patrick, describing a table of high-discharge U.S. rivers, wrote that data on discharge, drainage area, and length varied widely among authors whose works she consulted. "It seems," she said, "that the wisest course is to regard data tables such as the present one as showing the general ranks of rivers, and not to place too much importance on minor (10–20%) differences in figures."[9]
Table
The primary source for watershed and discharge data in the table below is Rivers of North America. Conflicting data from other sources, if the difference is greater than 10 percent, is reported in the notes. Discharge refers to the flow at the mouth.[n 1] In the "States, provinces, and image" column, the superscripts "s" and "m" indicate "source" and "mouth". Non-U.S. states appear in italics. Except in the "States, provinces, and image" column, abbreviations are as follows: "km" for "kilometer", "mi" for "mile", "s" for "second", "m" for "meter", and "ft" for "foot".
Key
River is not entirely within the United States.
Watershed is not entirely within the United States.
Dams, diversions for agriculture, and other human alterations to rivers have greatly affected the discharge of some rivers over time. For example, the virgin discharge of the Colorado River is estimated to have been 20,000ft3/s (566m3/s) compared to 1,400ft3/s (~40m3/s) in 2005.[10]
Of the total, 10,700mi2 (28,000km2), about two percent of the basin, is in Canada.[6][7]
Kammerer: 2,340mi (3,770km).[16]The Atlas of Canada: 2,348mi (3,779km).[6]
Of the total, 10,700mi2 (27,800km2), less than one percent of the basin, is in Canada.[6][7]
Of this total, 714mi (1,149km) are in Canada. This amounts to about 36percent of the main-stem length.[6]
The Atlas of Canada also lists the total basin size at 324,000mi2 (839,200km2), split between 125,000mi2 (323,800km2), about 39percent, in Canada and 199,000mi2 (515,400km2), about 61percent, in the United States.[6]
Kammerer: 1,900mi (3,100km).[16] University of Texas (UT): 1,799mi (2,895km).[24] The river forms the U.S.–Mexico border for 1.251mi (2,013km) (about 70percent of its main-stem length) from El Paso to the Gulf of Mexico.[24]
Rivers of North America says that of this total only about 170,000mi2 (450,000km2) of the basin contribute water to the river.[26] The University of Texas (UT) says, "The river collects rain, snowmelt and spring water from an area [of] about 215,338mi2 [557,722km2] including closed basins."[24] It says that 87,020mi2 (225,380km2) of the basin (about 48percent), not counting closed basins, are in Mexico, while 93,821mi2 (242,994km2) (about 52percent) are in the United States.[24] Kammerer cites a total basin size of 336,000mi2 (870,000km2).[16]
According to the Utah Division of Water Resources, 75mi (121km) of the river are in Mexico. This amounts to about 5percent of the main-stem length.[27] Of this, 17mi (27km) form the border between Mexico and the United States.[28]
The United Nations Environment Programme cites a total basin size of 246,000mi2 (637,000km2), split between 2,000mi2 (5,200km2) (about 1percent) in Mexico and 244,000mi2 (632,000km2) (about 99percent) in the United States.[28]
Derived by subtracting the length of the East Fork Arkansas River of roughly 16mi (26km)[31] from Kammerer's total of 1,459mi (2,348km).[16]
About 498mi (801km) are in Canada.[6] This amounts to about 40percent of the main-stem length.
The Atlas of Canada lists the total watershed at 259,200mi2 (671,300km2), split between 39,700mi2 (102,800km2) (about 15percent) in Canada and 219,500mi2 (568,500km2) (about 85percent) in the United States.[6] Kammerer's figure for the total watershed is 265,000mi2 (690,000km2).[16]
Also known as the Dakota River or Jim River and not to be confused with the James River of Virginia.
This is the average discharge for the years 1982–94, derived by adding the discharge for each of these years and dividing by 13.
According to The Canadian Encyclopedia, a 110-mi (170km) stretch of the river flows through Canada. This amounts to about 18percent of the main-stem length.[84]
The Atlas of Canada: 23,600mi2 (61,200km2) split between 8,300mi2 (21,600km2) (about 35percent) in Canada and 15,300mi2 (39,600km2) (about 65percent) in the United States.[6]
According to the U.S. Army Corps of Engineers, a 115-mi (185km) stretch of the river forms part of the U.S.–Canada border. This amounts to about 19percent of the main-stem length.[91]
Kammerer: 396,000mi2 (1,030,000km2).[16]The Atlas of Canada: 519,000mi2 (1,344,200km2), of which 324,000mi2 (839,200km2) (about 62percent) is in Canada and 195,000mi2 (505,000km2) (about 38percent) is in the United States.[6]
Of this total, 232mi2 (600km2) (about 0.4percent) are in the Mexican state of Sonora, and the rest is in the United States.[8]
Rivers of North America describes the discharge as less than 210ft3/s (6m3/s.
This is the size of the basin upstream of a stream gauge near Kindred and at river mile67.9 (river kilometer 109.3).[100]
This is the average flow measured by a stream gauge near Kindred and at river mile67.9 (river kilometer 109.3).[100]
The main-stem length is calculated by subtracting the length of the Nabesna River from Kammerer's total of 659mi (1,061km).[16] The Nabesna River is roughly 75mi (121km) long, calculated by adding the 60mi (97km) from the Nabesna mouth to Camp Creek[101] to the distance, 15mi (24km), from Camp Creek to Nabesna Glacier,[102] Kammerer's most remote source for the Tanana.
Reflects only that part of the basin above a stream gauge at river mile43.3 (river kilometer69.7) near Enterprise.[106]
Measured by a stream gauge at river mile43.3 (river kilometer69.7) near Enterprise.[106]
This is only a close approximation of the entire basin. It does not include a small fraction of the basin below the river gauge, located about 25mi (40km) upstream of the river mouth.
This is the average discharge for the years 1990–2010, derived by adding the discharge for each of these years and dividing by 21.
According to the Minnesota Department of Natural Resources, 394mi (634km) are in the United States. This amounts to about 72percent of the main-stem length.[116]
Of the total basin, 53,500mi2 (138,600km2) (about 48percent) are in Canada and 57,500mi2 (148,900km2) (about 52percent) are in the United States.[6]
The mouth coordinates and source coordinates are from the Geographic Names Information System (United States Geological Survey) or the Canadian Geographical Names Data Base except for the coordinates of the mouth of the Colorado River, derived by geolocating with Google Earth.
From Rivers of North America (ed. Benke and Cushing) unless otherwise noted.
Arias, E.; Albar, M.; Parra, I; Reza, M. "Regional Definition"(PDF). United Nations Environment Programme. pp.20–21. Archived from the original(PDF) on May 31, 2017. Retrieved May 30, 2017.
"Colorado River". Geographic Names Information System (GNIS). United States Geological Survey. February 8, 1980. Retrieved February 4, 2011.
Derived via Google Earth
Colorado Atlas and Gazetteer (Map). DeLorme. 1998. §47–48. ISBN978-0-89933-265-9.
"Arkansas River". Geographic Names Information System (GNIS). United States Geological Survey. November 30, 1979. Retrieved February 4, 2011.
Personius, Robert Giles; Eddy, Samuel (February 18, 1955). "Fishes of the Little Missouri River". Copeia. American Society of Ichthyologists and Herpetologists. 1955 (1): 41. doi:10.2307/1439450.
"Little Missouri River". Geographic Names Information System. United States Geological Survey (USGS). February 13, 1980. Retrieved February 23, 2011.
Benke, Arthur C.; Cushing, Colbert E. (2005). Rivers of North America. Burlington, Massachusetts: Elsevier Academic Press. ISBN978-0-12-088253-3.
Patrick, Ruth (1995). Rivers of the United States: Volume II: Chemical and Physical Characteristics. New York: John Wiley & Sons. p.24. ISBN978-0-471-10752-1.
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