The use of aluminum sulfate (alum) to precipitate phosphorus in highly eutrophic lakes is increasing. As use increases, the need to study the effects of alum on the biota increases. Possible adverse effects of alum on lake organisms may be due to chemical toxicity from dissolved aluminum compounds or to physical inhibition of movement, feeding, or reproduction from the precipitated aluminum hydroxide floc. Lethal and sublethal effects of alum on a wide range of fish and aquatic invertebrates described in the literature are reviewed. There is a lack of information as to the effects of alum on benthic insects. The objective of the study is to determine the acute and chronic effects of alum to Tanytarsus dissimilis. T. dissimilis is a representative of the Chironomidae, the family of organisms which occupies a significant portion of the benthic invertebrate community of lakes and which are important fish food organisms.