Study area
The study was conducted in Lake Baringo (Figure 1), a shallow (mean depth = ~ 9.5 m, Walumona, personal observation) freshwater lake in the eastern Rift Valley of Kenya. The lake lies at 0°36´N, 36°04´E, and approximately 60 km north of the equator at an altitude of 975 m above mean sea level. It is also a source of freshwater used for domestic purposes by the local population (especially for drinking), livestock and supports a substantial fishery in a semi-arid area. Its fishery has been reported to be poor and originally composed of five species. Three (Oreochromis niloticus baringoensis , Clarias gariepinus and Protopterus aetiopicus ) of species are of commercial value while, Barbus spp. now rarely appears in fisher’s catches and Labeo spp. has almost disappeared in the lake (Aloo, 2002). The decreased fish diversity is thought to be due to overfishing pressures but could also be attributed to limnological changes (Hickley et al ., 2004).
The lake surface is reported to cover slightly over 130 km2 with wide fluctuations as a consequence of water level fluctuations due to climatic influences (Kallqvist, 1987; Hickleyet al ., 2004). The catchment area is about 6820 km2 and includes a large part of the western escarpment of the Kenyan Rift Valley where most of the water is derived from.
The climate of the region is “semi-arid” characterized by two rainy seasons with an annual average of about 600 mm (Omondi et al ., 2014). Due to heavy rains experienced in 2011 in the Eastern African region, the lake water surface increased dramatically to 207 km2 in 2016 (Obando et al ., 2016) and then to more than 250 km2 in 2020. The dry season usually starts from September to February with no rain in January while, the rainy season occurs between March and August (Odada et al.,2006). The precipitation in the lake area ranges from about 600 mm on the east and south of the lake to 1500 mm on the western escarpment of the Rift Valley. Lake Baringo faces a very high annual evaporation rate of 1650-2300 mm (Odada et al ., 2006). The lake has no known outflow and is supplied by inflows from seasonal (Endao, Lokesen, Makutani, and Ol Arabe) and perrenial (Perkerra and Molo) rivers (Figure 1). Lake Baringo is believed to have an underground seepage that maintains its freshness by losing approximately 108 m3yr -1 (Dunkley et al ., 1993).