Aquatic biological communities were used to assess the biotic integrity of the Boise River upstream and downstream from the Lander Street and West Boise municipal wastewater treatment facilities (WTFs) in Boise, Idaho. Samples of epilithic periphyton, benthic macroinvertebrates, and fish were collected in late February and early March 1995, in late October 1996, and in early December 1996. Epilithic periphyton biomass, expressed as chlorophyll-a and ash-free dry weight, declined substantially between 1995 and 1996. Chlorophyll-a concentrations were higher at sites downstream from WTFs in both years, but differences in concentrations between sites upstream and downstream from WTFs were not statistically significant. High withinsite variance suggests that greater sampling intensity would improve statistical comparison. Index of Biotic Integrity (IBI) scores calculated for benthic macroinvertebrates were higher for the sites upstream from WTFs in 1995 and were the same for all sites in 1996. Similarly, IBI scores calculated for fish were higher for the sites upstream from WTFs in 1995, were higher for the site upstream from the Lander Street WTF in 1996, and were the same for sites upstream and downstream from the West Boise WTF in 1996. Two species of sculpin (Cottus) were abundant at the site upstream from both WTFs but were absent at all other sites downstream from WTFs in 1995 and composed only 2 percent of the total number of fish collected downstream from the Lander Street WTF in 1996.
