Toxicity of industrial effluents discharged directly into or in close proximity to the Trinity River (Tarrant County, Texas) was investigated through a 27-month period. The investigation was concerned with four aspects--bioassay, growth and development, chemistry, and benthos. Three industries contributed toxic materials which had a significant influence on the surrounding aquatic community. Toxicity ranges were established for the respective effluents using mature minnows, fry and spawn. Effluents from a railroad equipment cleaning area, a plant producing cracking catalysts used in processing combustion engine fuels, and a sewage treatment plant influenced the water quality of the river downstream from the outfalls. The ranges of nitrates, phosphates, biochemical oxygen demand and specific conductance for the river were increased by the effluents.