The Influence of the Clean Water Act and Tributaries on the Fish Community of the Big Sioux River, South Dakota

This study was initiated to l) compare fish communities in the Big Sioux River, South Dakota, between 1967 and 1994 and 2) investigate fish use of five tributaries as spawning and nursery areas. Fish species richness was higher in 1994 than in 1967. The greatest fish community changes between years, as indicated by low community similarity indices, were below Brookings and Sioux Falls, and in the lower river. Distributions of reproductive and feeding guilds were not different between years, however, some individual fish species distributions were different between years. Dissolved oxygen levels have increased and ammonia levels have decreased across years (1974-1994) at sites immediately below Brookings and Sioux Falls. However, such improvement was not found at a site near the mouth that represented the entire watershed. Levels of nitrate and phosphorus were higher since 1974. Other water quality parameters (i.e., suspended solids and fecal coliform) have not changed across years. Species migrating up tributaries to spawn were white suckers Catostomus commersoni and creek chubs Semotilus atromaculatus. Juveniles of both species were also abundant in tributaries. Juveniles of other species including northern pike Esox lucius, shorthead red horses Moxostoma macrolepidotum, and yellow perch Perea flayescens were also collected in tributaries. The results suggest that improvements in municipal waste treatment since the passage of the Clean Water Act in 1972 have improved the water quality below Brookings and Sioux Falls. However, increased levels of nitrate and total phosphorus suggests that nonpoint source pollution continues to degrade the majority of the river. The fish community may have responded favorably to improvements in water quality but some changes in the fish community could be due to higher stream discharges in 1994. Tributaries provided spawning and nursery habitat for some species including important recreational fish species. Controlling nonpoint-source pollution and protecting tributaries is important for maintaining and improving the fishery resources of the Big Sioux River