Fish communities were sampled at 6 tributary and 5 main stem sites in the South Platte River Basin (about 300 river miles) in August 1993 as a part of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program. The fish community structure of the South Platte River changed along elevation and temperature gradients from the mountains to plains. Mountain streams had fewer fish species than plains streams. Cool-water species, such as brown trout, rainbow trout, longnose sucker and longnose dace, were abundant at higher elevations (mountains), whereas warm-water species, such as common carp, white sucker and minnow and shiner species, were abundant in lower elevations (plains).
Of the six tributaries sampled, two were located in the mountains and four were located in the plains. Clear Creek at Golden, a site affected by upstream mining activity, had fewer fish species (2) and total fish (128) in a 150 meter reach than Cache la Poudre at the mouth of the canyon, a 179 meter reach, where 4 fish species and 297 total fish were collected. At Lonetree Creek near Greeley, a site affected by fluctuating agricultural return flows, no fish were present in a 191 meter reach compared to Lonetree Creek at Carr, an upstream rangeland site, where 4 species and 241 total fish in a 179 meter reach were collected. Cherry Creek at Denver, an urban tributary, had fewer species (5) and total fish (135) in a 157 meter reach compared to the main stem site, South Platte River at Denver, where 10 species and 2,005 total fish were collected in a 338 meter reach. The Saint Vrain River at the mouth near Platteville, a large plains tributary, had 11 species and 1,110 total fish in a 236 meter reach; this fish community was similar to the downstream main stem sites of the South Platte River.
The five sites sampled in the main stem of the South Platte River were located at Denver, Henderson, Kersey and Balzac all in Colorado, and at North Platte, Nebraska. In the main stem, the total number of fish species and number of individuals in a 230 to 300 meter reach increased in a downstream direction to North Platte. The number of fish species ranged from 9 at Denver and 7 at Henderson to 19 at North Platte. The total number of fish collected decreased in the South Platte River from Denver (2,005) to Henderson (178) and increased from Henderson to North Platte (2,536). White sucker and carp were present at all five main stem sites, whereas fathead minnow and creek chub were present at four of the five main stem sites. Cool-water species, such as longnose sucker and longnose dace, were abundant near Denver. Species associated with warm water, such as plains killifish, stoneroller, plains minnow, red shiner, shorthead redhorse and bigmouth shiner, were abundant at North Platte.
Fish community distribution was related to the natural elevational and temperature gradients characteristic of the South Platte River Basin. Land-use activities, such as mining and agricultural return flow, also seem to affect the fish communities in the basin.
1 U.S. Geological Survey, Box 25046, MS 415, Denver Federal
Center, Lakewood, CO 80225
2 Colorado Division of Wildlife