Lake Nakuru is a small, shallow, alkaline-saline lake located in a closed basin without outlets in the Eastern Rift Valley of equatorial East Africa. It is the centre of a most familiar national park of Kenya known for its spectacular bird fauna (495 species), particularly the vast flock of lesser flamingo (Phoeniconaias minor).

Being in the Rift Valley where tectonic and volcanic activities as well as climatic changes have been very remarkable, the lake underwent drastic changes during the recent geological ages. About 10,000 years ago, Nakuru and its two neighbor lakes, Elmenteita and Naivasha (60 km south of Nakuru), formed a single deep freshwater lake, which dried owing to the later desiccation of climate leaving the three separate lakes as remnants. The present maximum depth is about three meters, but the lake water level is still quite variable; the whole lake had been almost dried up several times during the past 50 years due to unknown reasons.

The lake is a soda-lake with a water pH value of 10.5 and an alkalinity of 122 meq l^-1. Main ions are sodium and bicarbonate-carbonate. The biota in the lake is very simple as in other saline lakes, consisting of phytoplankters dominated by blue-green algae and very poor planktonic and benthic fauna originally lacking fish. However, the lake is highly eutrophic owing to the vigorous growth of a planktonic blue-green alga, Spirulina platensis, which supports an immense number of alga-grazing lesser flamingo and an increasing population of the introduced fish, Sarotherodon alcalicum grahami, though, in the last several years since 1974, the planktonic productivity and the flamingo population decreased abruptly. The lake's catchment area amounts to some 1,800 km² and is extensively utilized for agriculture and livestock raising. The city of Nakuru on the northernmost shore of the lake is a rapidly growing local centre of industry and agriculture. Effluents from the city's two sewage treatment plants are discharged into the lake. The potential danger of pollution is suspected, but it is not yet clear whether the pollution is responsible for the recent changes of the lake ecosystem (1-8).