This fact sheet shows the location and ranking of the 20

largest rivers in the United States . It is common knowledge that

the Mississippi is the largest U.S . river, but what is the rank

of other major U.S . rivers? Rivers are considered large on the

basis of one or more of three characteristics : total length from

source to mouth, area of basin (watershed) drained by the stream,

and average rate of flow (discharge) at the mouth. The

alphabetical list on the back of this sheet shows these

characteristics of 32 rivers so as to include the 20 largest rivers

in each of the three categories . Among the 32 rivers, 16 are

tributary to other rivers on the list; the remaining rivers discharge

directly into oceans, seas, gulfs, or bays .

As dynamic parts of our environment, rivers and their

characteristics vary in space and time in response to climatic

changes and to man's activities . The causes include seasonal and

annual changes in precipitation and temperature, cycles

'

of

erosion and deposition (especially during floods), diversions of

water (for irrigation, power, and other purposes), and the

construction of public works-dams, levees, locks, and canals .

For example, combinations of these effects, but principally

diversions, have reduced the average flow of the Colorado River

near its mouth from about 22,000 cubic feet per second (ftl /s)

for the period 1903-34 to less than 4,000 ft'/s during the period

1951-80. However, the annual flow in 1984 averaged 17,500

ftl/s, a consequence of record-breaking precipitation on the river

basin. A flow of 1,000 ft l /s is equal to 646 million gallons per

day, 724,000 acre-feet per year, or 28 .3 cubic meters per

second . (One acre-foot is the volume of water that would cover

I acre to a depth of I foot .)

River lengths or river-length data are affected not only by

some of the natural and artificial causes noted in the preceding

paragraph, but also by the precision of various techniques of

measurement, by the scale of available maps or aerial photographs, and by somewhat arbitrary decisions. For example, the

length may be considered to be the distance from the mouth to

the most distant headwater source (irrespective of stream name)

or from the mouth to the headwaters of the stream commonly

identified as the source stream . The names of some rivers, such

as the Mississippi River and the Rio Grande, are unchanged from

source to mouth. In contrast, the name of the source of the

Mobile River-Tickanetley Creek-changes five times before

becoming Mobile River 45 miles north of Mobile Bay. The

lengths of meandering rivers, such as the Mississippi River south

of Cairo, Ill ., undergo significant changes in length from time

to time because of a natural or excavated cutoff (a channel severing a narrow strip of land, thus bypassing a large bend in a river)

that reduces river length and therefore navigation time . For

example, between 1766 and 1885, the length of the Mississippi

River from Cairo, Ill ., to New Orleans, La., was reduced by

218 miles because of 18 cutoffs (Elliott, 1932, page 59).

Reference cited-Elliott, D.O . (U .S . Mississippi River Commission),

1932, The improvement of the lower Mississippi River for flood

control and navigation : Vicksburg, Miss ., U.S . Waterways Experiment Station, U.S . Army Corps of Engineers, 345 pages.

For additional information write to :

U.S Geological Survey

Water Resources Division

MS 419, National Center

Reston, Virginia 22092
of the 32 rivers listed here the 20 largest in three categories-discharge, drainage basin, and length---are ranked from 1 to 20 these ranks are shown in parentheses .

Abbreviations : ft 3 /s=cubic feet per second ; mi l =square miles All data have been rounded to n o more than three significant figures . Sources of data : Stream

discharge and drainage area-mainly U .S Geological Survey reports and files ; length-publications and files of U .S . Geological Survey, U .S . Army Corps of Engineers, U .S . Environmental Protection Agency, and the Tennessee Valley Authority ; data for the St . Lawrence River from "Facts from Canadian Maps," Canada

Department of Energy, Mines and Resources, 1972 . Period of record for most rivers is 1951-80 Some data are provisional, and subject to revision . Compiled bY

J .C . Kammerer, U .S Geological Survey

!VOTE Rank from 1 to 20 in each category is shown in parentheses .