Sites - Important Bird and Biodiversity Areas (IBAs)
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Kenya, Rift Valley Province
36o 21.00' East 0o 46.00' South
A1, A2, A4i, A4iii
Year of IBA assessment
Site description This site lies on the floor of the Rift Valley, 80 km north-west of Nairobi, and consists of a shallow freshwater lake (15,600 ha) and its fringing Acacia woodland (c.7,000 ha). Lake Naivasha is of recent geological origin, and is ringed by extinct or dormant volcanoes, including Mounts Longonot, Ol Karia and Eburu. Naivasha’s water is supplied by the permanent Malewa and Gilgil rivers, which respectively drain the Aberdare mountains (IBA KE001) and the Rift Valley floor to the north, by the seasonal Karati river (also draining from the Aberdares) and from substantial ground-water seepage. The Malewa covers 1,730 km2 of the 2,800 km2 catchment, and contributes 90% of the surface water entering the lake. Naivasha has no surface outlet. It is thought that a combination of underground outflow and sedimentation of salts keeps the lake fresh, unlike other endorheic lakes in the eastern Rift Valley. Naivasha includes three chemically distinct water bodies. The main lake (c.15,000 ha, maximum depth c.8 m) incorporates a partially submerged crater, the Crescent Island lagoon (maximum depth c.18 m), at its eastern end. The lagoon is largely isolated at low water levels. To the south-east, separated by papyrus Cyperus papyrus swamp and an isthmus of Acacia woodland, is the small (c.550 ha), somewhat alkaline Lake Oloidien. Papyrus fringes the main lake’s shore (with scatterings of other sedges and Typha) and cloaks the inlets of the Gilgil and Malewa rivers. There are large floating, wind-driven rafts of the exotic water-hyacinth Eichhornia crassipes, usually concentrated in the south-west sector. Submerged macrophytes (including Potamogeton spp. and Naja pectinata) sometimes occur in large beds, mainly in the shallow eastern part, but these vary greatly in extent. The shores of Crescent Island lagoon are steep and rocky or flat and muddy, while Oloidien has an open, grassy shoreline, with no emergent or floating macrophytes. The lake’s levels fluctuate enormously, and Naivasha has been dry within historic times. The surrounding riparian land is almost all privately owned, much of it now used for intensive horticulture and floriculture using water from the lake. A belt of tall Acacia xanthophloea woodland fringes the lake and extends along the rivers to the north, though portions have been cleared for farming; further from the water this gives way to dry open grassland, Tarchonanthus camphoratus scrub and (on rocky hillsides) Euphorbia forest. Naivasha is the second site listed by Kenya as a Wetland of International Importance under the Ramsar Convention.
Key Biodiversity See Box and Table 2 for key species. The woodland north of the lake and around Lake Oloidien provides habitat for Prionops poliolophus, which has been recorded here regularly and is known to nest. Acrocephalus griseldis is a winter visitor and passage migrant, the exact status of which is unknown. The lake itself supports a diverse waterbird community, with more than 80 species regularly recorded during censuses. Mean numbers during 1991–2001 were 19,600 waterbirds. Depending on water levels, it can be a significant site for Fulica cristata (mean 5,050 during 1991–2001), Platalea alba (mean 138 during 1991–2001) and Tachybaptus ruficollis (mean 650 during 1991–2001). Many species of duck and Palearctic waders also occur in numbers; Palearctic duck are especially abundant in November and February. Phoenicopterus minor occurs in small numbers at times, mainly on Oloidien. The lake is known for its high density of Haliaeetus vocifer, which nest in the surrounding Acacia woodland. Regionally threatened species include Podiceps cristatus (most recent Kenyan records are from Oloidien, with seven birds seen in January 1996); Oxyura maccoa (regular on Oloidien, with 170 in January 1994 and January 1997); Anhinga rufa (one recorded on Oloidien in January 1997); Casmerodius albus (regular at Naivasha, which is an important feeding site; 73 counted in January 1997); Ephippiorhynchus senegalensis (2–3 birds usually present); Thalassornis leuconotus (occasional; 12 counted on Oloidien in January 1994); Porzana pusilla (status uncertain); and Rynchops flavirostris (irregular visitor). Since 1995 a large nesting colony of Phalacrocorax carbo has established itself in the fringing Acacia woodland at Lake Oloidien.
Non-bird biodiversity: The lake supports a large and expanding population of Hippopotamus amphibius (c.300 individuals at present). The snake Bitis worthingtonii, endemic to the central Rift Valley above 1,500 m, is recorded from Naivasha.