Lakes and riparian biodiversity
The Lake Naivasha Basin is the highest lake basin in the entire Rift Valley, which has more than 20 lakes between Mozambique and the Red Sea, spanning an altitudinal gap going from 1880 to 4000 m. The lake is formed from several spent volcanic craters, five of them are clearly visible from maps and satellite photographs. Three ancient calderas are filled with freshwater and form Lake Naivasha (including Crescent Island Lagoon, the Main Lake crater and another one in proximity of Hippo Point), one is brackish (Lake Oloidien) - currently jointed to the Main Lake - and one is hypersaline (Lake Sonachi). The rivers, riparian wetlands and artificial reservoirs in the basin, give the whole a large number of water body types, yet despite this it has a moderate fish biodiversity.
The lake (0°45 0 S, 36°20 0 E) is at 1890 m a.s.l., its shoreline extends about 120-150 km, its average water depth is around 3 m, with deeper parts reaching 7 m (but 18 m in the small Crescent Island crater sub-basin). All these figures are variable, because the water level can vary by about 3 vertical metres a decade, so any published account of the lake should always state the year that the figures refer to.
Naivasha's freshwater is distinctive in the Rift Valley, where all lakes lack an exit and most are saline. This characteristic , together with its hydrological unpredictability, leads to a 'drawdown zone' surrounding the water, which permits a high density of semi-aquatic (hippo, coypu, otters, mongooses) riparian (waterbuck, wildebeest, buffalo) and terrestrial (Thompson's gazelle, zebra, giraffe, warthog) ungulates, as well as of other mammal species (vervet and black and white colobus monkeys, baboon, hyaena) living along the lake shores.
The permanent inflow of water to the lake from the Malewa river is ensured by the high mountain ridges and plateaux (>3000 m) to the East and North-West, which act as „water towers“. The major tributaries reach the lake from the North and East, while the South and West are covered with dry savannah and intermittent streams.
The littoral edge of the lake is the most species rich, dominated by floating papyrus, but with many other floating and shallow rooted water plants. These support a diverse aquatic bird community as well as the substantial population of hippopotamus. However, the lake surface is overall dominated by alien floating plants, such as water hyacinth Eichhornia crassipes and water fern Salvinia molesta.
- Fish community
- Original aquatic biodiversity
- Floating plants
- Lakeshore birds
- Riparian forests
- Fringing papyrus