The Arkansas River originates near the Continental Divide in Central Colorado and then flows eastward through the city of Pueblo and on across the plains. As the river passes through the city of Pueblo it is diverted for various industrial and irrigation uses and, in return, it receives discharges from several sources. Two of the major sources of waste discharges are the Northside and Southside Water Treatment Plants. Each of these plants has large settling ponds used to contain the sludges produced during the chemical treatment of river water for potable use. Once each year during a two to three week period these plants dispose of the accumulated solids by flushing them directly into the Arkansas River. In order to assess the impact of these two water treatment plant discharges on the Arkansas River, the Technical Support Branch of the Regional EPA office conducted a study on October 10-12, 1972, during the period of pond discharge. The basic objective was to determine whether the solids in the discharges were of sufficient magnitude to cause benthic organism and water quality degradation in violation of the Colorado Water Quality Standards. The study included chemical and biological sampling conducted at four river stations in a three mile stream reach in the area of the water treatment plants. The two pond discharges were also sampled for chemical analysis.