As part of the U.S. Geological Survey National Water-Quality Assessment (NAWQA) program, fish communities were sampled at five sites in the South Platte River from Denver, Colorado, to North Platte, Nebraska. The number and composition of fish species changed from upstream to downstream in the South Platte River. The total number of fish collected at each site varied among sites and from year to year.
FS-154-95 (PDF Version - 90 Kb)
The NAWQA program uses an integrated approach (physical, chemical, and biological) to assess water quality on a basin-wide scale. Multiple lines of evidence are used in assessing water-quality conditions at a site. A goal of the South Platte NAWQA study is to provide a basin-wide assessment of the status and variability of stream biological communities to assist in the assessment of water quality in the basin. A first step in understanding how fish communities are related to water quality is to examine the changes in fish occurrence and distribution in the basin.
A fish community is a group of fish species that inhabit the same area and interact with each other. The structure of a fish community is determined by the species present; their relative abundances, life stages, and size distribution; and their distribution in space and time.
Figure 2 -- Location of sampling sites along the South Platte River.
Fish communities were sampled at five sites along the South Platte River from Denver to North Platte during August 1993 and 1994. Fish communities were collected with the assistance of individuals from the U.S. Fish and Wildlife Service, the National Biological Service, and the Colorado Division of Wildlife. Fish were collected from a section of stream about 250 to 325 yards in length using electrofishing techniques. During electrofishing, a probe emitting a localized electrical current (generally extending no greater than 4 feet around the probe) is placed in the water. Fish are attracted to the electrical current and become momentarily stunned and are netted. The total number of each fish species was counted, and the length and weight of as many as 30 fish of each species were measured. After counting and weighing, the fish were released back into the river.
A greater number of fish were collected at each site in 1993 than in 1994. Catching fish at any one site is not an exact procedure. Numbers of fish and the types of fish species collected can vary from month to month because of many factors, including the amount of streamflow, the visibility of fish in water at the time of collection, and the mobility of the fish. Although the number of fish at a site varied between 1993 and 1994, the pattern among sites was similar among the two sampling periods. The Henderson, Colorado, site had the lowest number of fish, and the North Platte, Nebraska, site had the highest number of fish.
Figure 3 -- Number of fish collected at sites in the South Platte River.