Bogoria is a narrow, shallow, alkaline lake on the Rift Valley floor, varying from 3,000 to 4,250 ha in extent, with a maximum depth of 8.5 m. To the east, the Siracho escarpment rises abruptly from the lakeshore, while on the relatively flat western shore is a series of spectacular hot springs and geysers. The reserve was gazetted in 1981 and includes the entire lake and its immediate surroundings. The waterusually supports a dense bloom of the cyanophyte Spirulina sp. The terrestrial vegetation is mainly thorny bushland, dominated by species of Acacia, Balanites and Commiphora, with patches of riverine woodland containing Ficus capensis, Acacia xanthophloea and A. tortilis. The open shore, often littered with lava boulders, is dominated by alkaline-tolerant grasslands of Sporobolus spicatus, with the sedge Cyperus laevigatus around the hot springs. The lower slopes of the Siracho escarpment are covered by Combretum and Grewia thicket. The lake is fed by its springs and by the Sandai (or Waseges) river, which rises on the eastern scarp of the Rift Valley. The Sandai flows past the lake and then turns through 180° to enter it from the north through the Kisibor swamp, a sizeable freshwater wetland dominated by Typha.
See Box for key species. Bogoria is a key feeding ground for the itinerant Rift Valley population of the Near Threatened Phoenicopterus minor. Spectacular congregations (estimated at up to 2 million birds) occur at times, and several hundred thousand birds are often present, with numbers fluctuating less than on other Rift Valley lakes. Although large numbers of very young birds may be present at times, this species has not bred successfully here. Podiceps nigricollis and Anas capensis are usually present in good numbers. The 10 year (1992–2001) January mean for waterbird numbers was 542,200, with a maximum of 1,078,400 recorded in January 1999. An estimate of 1.5 million birds (primarily flamingos) was made for July 1994. Thirty-one of Kenya’s 94 Somali–Masai biome species occur in the bushland and woodland around the lake. Other species of global conservation concern recorded at Bogoria include Circus macrourus (on passage) and Falco naumanni (also on passage, but in small numbers). Regionally threatened species include Podiceps cristatus (no recent records); Anhinga rufa (has occurred in swamp to north of lake); Oxyura maccoa (no recent records); Thalassornis leuconotus (no recent records); Trigonoceps occipitalis (status uncertain); and Polemaetus bellicosus (probably resident).
Non-bird biodiversity: The hot springs contain a highly specialized microbial fauna, with several endemic species.
Pressure/threats to key biodiversity
Lake Bogoria is spectacular. The extraordinary hot springs and geysers, the rugged faulted landscape, the huge numbers of flamingos and the chance of seeing greater kudu are great attractions for visitors. At present, tourists exert no obvious pressure on the environment at Bogoria. The Koibatek County Council manages the reserve but its existence is not free of controversy, with some local people claiming that they are not benefiting adequately from the income that it generates. A symptom of this is that cattle grazing and human settlement have recently become evident within the reserve’s boundaries and are steadily increasing. Mass deaths of Phoenicopterus minor have occurred on and off in recent years. The reasons for this are still unclear, though the birds seem to be succumbing to a stress-related infectious disease. It has been suggested that a contributory factor may be heavy metal pollution of their feeding grounds at Lake Nakuru (IBA KE045), but there is little direct evidence for this. The hydrology of Bogoria is poorly understood, but the rivers and springs that feed the lake are likely to be affected by extensive deforestation and land degradation within the catchment.
BirdLife International (2017) Important Bird Areas factsheet: Lake Bogoria National Reserve. Downloaded from
http://www.birdlife.org on 12/12/2017.