This study was carried out from April 1999 to May 2000 to investigate the extent of pollution of Lake Nakuru. Water, sediment, fish and algae collected from the lake and its feeder rivers during the dry and rainy seasons were analysed for heavy metals and organochlorine pesticide residues to identify possible sources of contaminants. Atomic absorption spectrophotometry and gas chromatography showed that more contaminants were added to the lake during the rainy season than the dry season. Heavy metals and pesticide residues were found in higher concentrations in the sediments than in the water. Contamination by most of the pollutants has increased over the past 25 years. DDD is more prevalent in the sediments and particulates in the water, but DDE is predominant in fish, suggesting two different mechanisms of DDT degradation in the biotic and abiotic environments. Whereas heavy metals tend to be distributed almost uniformly within the lake, pesticide residues are found predominantly in its northern and southern river inlets. Some contaminants occur in slightly higher concentration upstream, perhaps due to contamination from point sources, followed by dilution.