The study refers to the composition of the zoobenthos in submerged macrophytes in Lake Nemi, subject to an organic pollution caused mainly by domestic wastes. The fauna, sampled in five stations in the period 1981/82, was composed of 18 zoological groups, including 60 taxa. Cladocera, represented almost exclusively by the microfiltratorChydorus sphaericus, constituted by far the dominant group in all stations. Oligochaeta, comprising 14 taxa, was the most diversified group and their maximum percentages ware found in the Genzano village discharge. Other detritivorous groups, such as Chironomidae and Ostracoda were also abundant, while Hydroida and some Cyclopidae were the most common predator organisms. Owing to the eutrophication process, we can observe: a) abundance of species having wide ecological valence; b) low diversification and reduced abundances in most of the zoological groups; c) prevalence of a detritus food chain.