Site description This is a complex of wetlands in the delta of the Yala river, on the north-east shore of Lake Victoria. The site has three main components: the Yala swamp itself (currently c.6,500 ha after drainage of the eastern 20%); Lake Kanyaboli in the north-eastern corner, a 3-m deep lake of c.1,000 ha; and Lake Sare, the most southerly of several outlets of the Yala river into Lake Victoria, c.5 m deep and 500 ha in area. Formerly, the Yala river flowed through the eastern swamp (now ‘reclaimed’) into Lake Kanyaboli, then into the main swamp, and finally into Lake Victoria via a small gulf. The Yala flow is now diverted directly into the main swamp, and a silt-clay dike cuts off Lake Kanyaboli, which receives its water from the surrounding catchment and through back-seepage from the swamp. A culvert across the mouth of the Yala, some metres above the level of Lake Victoria, has cut off the gulf on the lake and, through back-flooding, created Lake Sare. Water in the main channels and lakes is well oxygenated, but oxygen levels in the stagnant parts of the swamp are low. The predominant vegetation is papyrus Cyperus papyrus, with Phragmites mauritianus in shallower areas and swamp grasses around the periphery. A thick fringe of papyrus surrounds both Lake Kanyaboli and Lake Sare; in the case of Lake Sare, this merges with the main swamp. The Yala swamp complex is by far the largest papyrus swamp in the Kenyan sector of Lake Victoria, making up more than 90% of the total area of papyrus. The swamp acts as a natural filter for a variety of biocides and other agricultural pollutants from the surrounding catchment, and also effectively removes silt before the water enters Lake Victoria. The site supports an important local fishery for the Luo and Luhya people who live to its south and north, respectively.
Key Biodiversity See Box and Table 3 for key species. Yala swamp supports sizeable populations of Chloropeta gracilirostris (common in tall, undisturbed stands of fringing papyrus, especially at Lake Kanyaboli) and Laniarius mufumbiri. The Near Threatened Gallinago media, a Palearctic migrant, probably also occurs. Because of its size and the generally good condition of the papyrus, the Yala swamp complex is an important site for East Africa’s papyrus endemics. These include Chloropeta gracilirostris, Cisticola carruthersi, Bradypterus carpalis and Serinus koliensis. Many other wetland birds also occur. Reports of occasional sightings of Balaeniceps rex by the local residents have not been confirmed. Regionally threatened species include Casmerodius albus (present in small numbers) and Porzana pusilla (recorded from Lake Kanyaboli, but may not be resident).
Non-bird biodiversity: Lake Kanyaboli is an important refuge for Lake Victoria cichlid fish, many of which have been exterminated in the main lake by the introduction of the non-native predatory fish Lates niloticus. These include economically important species such as Oreochromis esculentus (VU), as well as a number of Haplochromis species. Lates niloticus is present in Lake Sare, which has an impoverished fish fauna compared to Kanyaboli.