Hydrobiological events in Nyumba ya Mungu reservoir, a recent man‐made lake in Tanzania, are reviewed in the light of those described for larger impoundments in other parts of Africa. An initial phase of rapid eutrophication and of high fish production has been replaced by a slower stabilization phase. At present the inflowing rivers supply a nutrient rich water and the level of primary production remains high. In spite of the risk of an encroachment ofTypha domingensisacross the shallow end and events associated with overfishing, the lake retains most of the essential requirements to continue as a useful tilapia fishery. The introduction of new fish into the reservoir, to fill gaps in the trophic structure of the fish community is not recommende