This is a shallow alkaline lake, its surface largely covered by crusts of sodium carbonate, 85 km south-west of Nairobi in a low-lying basin on the floor of the Rift Valley. Extensive surface water is present only after heavy rains over the local catchment, when run-off reaches the northern end of the lake via three wadis. Most of the lake is a vast expanse of solid sodium carbonate (trona) and allied salts, some 15–30 m thick. This is mined by the Magadi Soda company, whose factory and associated town are on the north-eastern shore. The lake’s main basin is 29 km wide and oriented almost due north-south; the north-west arm is 12 km long and 2.5 km wide. The lake is surrounded and fed with water by a number of hot springs that feed shallow, permanent lagoons at the northern, southern and western extremities (other springs well up invisibly below the surface). These warm lagoons are carpeted with cyanophytes, which are grazed upon by shoals of the fish Oreochromis alcalicus grahami. The climate is inhospitably hot and arid (mean maximum temperatures c.35°C, rainfall c.400 mm/year), and the vegetation surrounding the lake is sparse, open bushland.
See Box for key species. Bird life is concentrated at the lagoons. Phoenicopterus minor is often present in internationally important numbers (mean January count, 1994–2001 (seven years): 23,250), though Magadi is a much less significant feeding site for this species than Bogoria (IBA KE045) or Nakuru (KE049). Very large numbers of this species may breed here on rare occasions, perhaps once a century: the last such event was in July 1962, when over a million pairs were nesting. A good variety of other waterbirds is present, including a sizeable resident population of Charadrius pallidus (mean count 1994–2001: 420). Mean total waterbird numbers in January for between 1994–2001 were 25,800. Other birds nesting at Magadi include Platalea alba, Anas capensis, Recurvirostra avocetta and Himantopus himantopus. Many Palearctic migrant waders winter here too, notably Calidris minuta. The bushland around the lake supports 28 of Kenya’s 94 Somali–Masai biome species. Casmerodius albus, a regionally threatened species, is an occasional visitor.
Non-bird biodiversity: The cichlid fish Oreochromis alcalicus grahami, endemic to alkaline lakes in this part of the Rift Valley, is abundant in the hot springs. The springs also contain a highly specialized microbial fauna, with several endemic species.
Pressure/threats to key biodiversity
The lake is unprotected and is commercially mined for sodium carbonate (which appears to be replenished at least as fast as it is removed). Removal of trona takes place from an area not used by waterbirds, and appears to have minimal impact on wildlife. Magadi faces no obvious conservation problems at present.