Top 10 Largest Rivers in the United States by Average Discharge
The ten rivers with the greatest average flow at the mouth in the USGS table Largest Rivers in the United States (rev. May 1990), which counts the St. Lawrence-Great Lakes system: from the Mississippi (593,000 ft³/s) to the Copper (59,000 ft³/s).
Updated October 23, 202610 ranked1 sources
Quick answer
The Mississippi River is the largest river in the United States by average discharge, at 593,000 ft³/s at its mouth. The St. Lawrence River is second at 348,000 ft³/s and the Ohio River third at 281,000 ft³/s. The ranking uses average discharge at the mouth from the USGS fact sheet Largest Rivers in the United States (rev. May 1990), with most records covering 1951-80.
How big is a river? The U.S. Geological Survey considers a river large on the basis of one or more of three characteristics: length from source to mouth, the area of the basin it drains, and the average rate of flow, or discharge, at its mouth. This list uses discharge, the volume of water passing the river's mouth, in cubic feet per second (ft³/s).
The figures come from a single USGS fact sheet, Largest Rivers in the United States by J.C. Kammerer (Open-File Report 87-242, revised May 1990). It is an old table: the period of record for most rivers is 1951-80, and USGS notes that river flows change over time with climate and with diversions, dams and other works.
Average discharge at mouth (ft³/s)
Average discharge at mouth (ft³/s)
Mississippi River
593000 ft³/s
St. Lawrence River
348000 ft³/s
Ohio River
281000 ft³/s
Columbia River
265000 ft³/s
Yukon River
225000 ft³/s
Missouri River
76200 ft³/s
Tennessee River
68000 ft³/s
Mobile River
67200 ft³/s
Kuskokwim River
67000 ft³/s
Copper River
59000 ft³/s
The ranking
1
Mississippi River
The Mississippi averages 593,000 ft³/s at its mouth in Louisiana, 245,000 ft³/s more than the second-place St. Lawrence. The USGS figure excludes the Atchafalaya-Red River basin; the table's footnote puts the whole Mississippi system, including the Atchafalaya, Red and Missouri basins, at 651,000 ft³/s. It also ranks first in drainage area and second in length.
Location of mouth: LouisianaDrainage area: 1,150,000 mi² (U.S.-Canada)Length (source to mouth): 2,340 miSource stream: Mississippi River, Minnesota (Clearwater County)
2
St. Lawrence River
The St. Lawrence, listed by USGS as the St. Lawrence-Great Lakes system, averages 348,000 ft³/s. Its mouth is in Canada and its drainage area is shared by the U.S. and Canada; the table takes its data from a Canadian government publication, Facts from Canadian Maps (1972).
Location of mouth: CanadaDrainage area: 396,000 mi² (U.S.-Canada)Length (source to mouth): 1,900 miSource stream: North River, Minnesota (Lake County)
3
Ohio River
The Ohio averages 281,000 ft³/s at its mouth (Illinois-Kentucky), the most of any river in the table whose drainage area is not marked as shared with Canada or Mexico. It drains 203,000 mi² and runs 1,310 miles from its source stream, the Allegheny River in Pennsylvania.
Location of mouth: Illinois-KentuckyDrainage area: 203,000 mi²Length (source to mouth): 1,310 miSource stream: Allegheny River, Pennsylvania (Potter County)
4
Columbia River
The Columbia averages 265,000 ft³/s at its mouth (Oregon-Washington). Its 258,000 mi² drainage area spans the U.S. and Canada, and its source stream is in British Columbia.
Location of mouth: Oregon-WashingtonDrainage area: 258,000 mi² (U.S.-Canada)Length (source to mouth): 1,249 miSource stream: Columbia River, British Columbia, Canada
5
Yukon River
The Yukon averages 225,000 ft³/s at its mouth in Alaska, the largest discharge of the eight Alaska rivers in the table. It is also the third-longest river in the table at 1,980 miles, measured from the McNeil River in Canada's Yukon Territory.
Location of mouth: AlaskaDrainage area: 328,000 mi² (U.S.-Canada)Length (source to mouth): 1,980 miSource stream: McNeil River, Yukon Territory, Canada
6
Missouri River
The Missouri averages 76,200 ft³/s at its mouth in Missouri, a steep drop from the Yukon's 225,000 ft³/s. It is the longest river in the table at 2,540 miles and second in drainage area at 529,000 mi²; the USGS footnote counts its basin as part of the Mississippi River system.
Location of mouth: MissouriDrainage area: 529,000 mi² (U.S.-Canada)Length (source to mouth): 2,540 miSource stream: Red Rock Creek, Montana (Beaverhead County)
7
Tennessee River
The Tennessee averages 68,000 ft³/s at its mouth in Kentucky from a drainage area of 40,900 mi², a smaller basin than any other river in this top 10 except the Copper.
Location of mouth: KentuckyDrainage area: 40,900 mi²Length (source to mouth): 886 miSource stream: Courthouse Creek, North Carolina (Transylvania County)
8
Mobile River
The Mobile averages 67,200 ft³/s at its mouth in Alabama, just ahead of the Kuskokwim. USGS notes that the name of its source, Tickanetley Creek in Georgia, changes five times before it becomes the Mobile River 45 miles north of Mobile Bay.
Location of mouth: AlabamaDrainage area: 44,600 mi²Length (source to mouth): 774 miSource stream: Tickanetley Creek, Georgia (Gilmer County)
9
Kuskokwim River
The Kuskokwim averages 67,000 ft³/s at its mouth in Alaska, just behind the Mobile (67,200 ft³/s). Its source stream is the South Fork Kuskokwim River at the terminus of an unnamed glacier.
Location of mouth: AlaskaDrainage area: 48,000 mi²Length (source to mouth): 724 miSource stream: South Fork Kuskokwim River at terminus of unnamed glacier, Alaska
10
Copper River
The Copper averages 59,000 ft³/s at its mouth in Alaska, just ahead of the Atchafalaya (58,000 ft³/s), which is 11th. It is the shortest river in this top 10 at 286 miles, rising at the terminus of Copper Glacier.
Location of mouth: AlaskaDrainage area: 24,400 mi²Length (source to mouth): 286 miSource stream: Copper River at terminus of Copper Glacier, Alaska
Full comparison
#
Name
Location of mouth
Drainage area
Length (source to mouth)
Source stream
1
Mississippi River
Louisiana
1,150,000 mi² (U.S.-Canada)
2,340 mi
Mississippi River, Minnesota (Clearwater County)
2
St. Lawrence River
Canada
396,000 mi² (U.S.-Canada)
1,900 mi
North River, Minnesota (Lake County)
3
Ohio River
Illinois-Kentucky
203,000 mi²
1,310 mi
Allegheny River, Pennsylvania (Potter County)
4
Columbia River
Oregon-Washington
258,000 mi² (U.S.-Canada)
1,249 mi
Columbia River, British Columbia, Canada
5
Yukon River
Alaska
328,000 mi² (U.S.-Canada)
1,980 mi
McNeil River, Yukon Territory, Canada
6
Missouri River
Missouri
529,000 mi² (U.S.-Canada)
2,540 mi
Red Rock Creek, Montana (Beaverhead County)
7
Tennessee River
Kentucky
40,900 mi²
886 mi
Courthouse Creek, North Carolina (Transylvania County)
8
Mobile River
Alabama
44,600 mi²
774 mi
Tickanetley Creek, Georgia (Gilmer County)
9
Kuskokwim River
Alaska
48,000 mi²
724 mi
South Fork Kuskokwim River at terminus of unnamed glacier, Alaska
10
Copper River
Alaska
24,400 mi²
286 mi
Copper River at terminus of Copper Glacier, Alaska
How we ranked this
Rivers are ranked by the 'Average discharge at mouth' column of the USGS fact sheet Largest Rivers in the United States, by J.C. Kammerer (Open-File Report 87-242, rev. May 1990), the only source for figures on this page. The table lists 32 rivers chosen to cover the 20 largest by discharge, drainage area and length. It gives discharge in thousands of ft³/s (multiplied out here) and shows each river's discharge rank from 1 to 20 in parentheses; our order follows the discharge column across the whole table and matches those ranks. Rivers marked * in the source carry less than 15,000 ft³/s and are not ranked. Rivers are counted as USGS counts them: the table includes tributaries alongside main stems (16 of its 32 rivers are tributary to other rivers on the list), the Mississippi figure excludes the Atchafalaya-Red River basin, the Atchafalaya figure (58,000 ft³/s, 11th) excludes about 167,000 ft³/s diverted from the Mississippi, and the St. Lawrence-Great Lakes system is included although its mouth is in Canada. Drainage areas are marked U.S.-Canada or U.S.-Mexico as in the source. The period of record for most rivers is 1951-80; USGS rounds all data to no more than three significant figures and says some data are provisional and subject to revision. There are no ties in the top 10. Drainage area, length and source stream come from the same table.
FAQ
What is the largest river in the United States by discharge?
The Mississippi River, averaging 593,000 ft³/s at its mouth in Louisiana in the USGS table. For the whole Mississippi system, including the Atchafalaya, Red and Missouri basins, the USGS footnote gives 651,000 ft³/s.
Why is the St. Lawrence on a list of U.S. rivers?
USGS includes the St. Lawrence-Great Lakes system in its table of the largest U.S. rivers and ranks it second by discharge, at 348,000 ft³/s. Its mouth is in Canada, its drainage area is shared by the U.S. and Canada, and its data come from a Canadian government source.
Is the Missouri River bigger than the Mississippi?
Longer, but not bigger by flow. In the USGS table the Missouri is the longest river at 2,540 miles against the Mississippi's 2,340, but it averages 76,200 ft³/s at its mouth against the Mississippi's 593,000 ft³/s.
How old are these figures?
The USGS fact sheet was revised in May 1990, and the period of record for most rivers is 1951-80. USGS notes that some data are provisional and subject to revision.
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