Effects of ammonia and chlorine on fish in streams receiving secondary discharges

Three Illinois streams receiving secondary wastewater were monitored monthly for 20 months. Copper Slough and Saline Branch received an effluent directly from a treatment plant, and Kaskaskia Ditch received an effluent from Copper Slough, its tributary stream. The effluents were chlorinated only during the first 11 months of the study. Fish communities in the reaches of all three streams suffered degradation while chlorination was practiced. After chlorination was discontinued, number of fish species below the outfall in Copper Slough and in Kaskaskia Ditch below the Copper Slough confluence increased markedly, and in terms of species number was equal or superior to the fish community above the confluence. Recovery was delayed in Saline Branch because of severe effluent quality problems associated with the renovation of the treatment plant discharging into this stream, but eventually was complete.