Gilderhus, P. A., Bills, T. D., and Johnson, D. A., 1992, Methods for detoxifying the lampricide 3-trifluoromethyl-4-nitrophenol in a stream, U.S. Fish and Wildlife Service Resource Publication 184: Washington, D.C., U.S. Fish and Wildlife Service, 5 p. Abstract Two methods to detoxify the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) were tested n the laboratory. Application of 30 to 50 mg/L of activated carbon, applied as an aqueous slurry, removed enough TFM from the water to detoxify most sea lamprey control treatments. Because the toxicity of TFM decreases as the pH of water increases, we also tested the application of sodium hydroxide (NaOH) to raise the pH of the water. Raising the pH by 1.5 units partly detoxified concentrations of TFM applied in lamprey control. A small tributary of the Sturgeon River, Delta County, Michigan, was treated with 6.5 mg/L TFM. Caustic soda to raise the pH of the stream was applied a short distance downstream. All caged rainbow trout (Oncorhynchus mykiss ) died in the reach with TFM but none died downstream of the raised pH. Raising the pH of the stream detoxified TFM enough to reverse an ongoing major kill of nontarget fishes. Keywords fresh-water, pesticides, detoxification, pH-effects, freshwater-pollution, pH, lampricides-