Eight species of Crustacea and 28 species of Rotifera were identified in zooplankton samples from Nyumba ya Mungu reservoir. In all localities the dominant organism was the copepodThermocyclops hyalinus.Cladocerans and rotifers made a variable contribution. Insects, among which the Chironomidae were pre‐eminent, formed the major component of littoral macroinvertebrate communities. Oligochaetes, crustaceans and gastropods, including vectors of Schistosomiasis, were rare or restricted in distribution. In contrast to the deep end of the lake, where submerged trees were the poorest substrate, those at the shallow end supported a high biomass of invertebrates, since prolonged exposure had accelerated rotting and facilitated colonisation by the burrowing nymphs ofPovilla.The variety of invertebrates on stony and muddy shores was increased when rooted emergent plants were present. The richest benthic community was found in submerged beds ofCeratophyltum.It is suggested that drawdown and the restricted development and movement of floating vegetation, have limited the spread of gastropods in the lake. Zooplankton, chironomid larvae and pupae, and ephemeropteran nymphs were shown to be important in the diet of small carnivorous and omnivorous fish specie