The LVS Basin has a catchment area of 26 906 km2 and is in the western part of the country. It borders Tanzania to the South and Lake Victoria to the East. The major towns in the Basin are Kisumu, Kisii, Migori, Kericho, Homa Bay, Bomet and Kehancha.
The Basin receives the second highest rainfall in the country, after the LVN Basin. The LVS Basin topography ranges from the Mt. Londiani peak at 3 000 masl to the shores of Lake Victoria at 1 130 masl. The basin is characterised by the Nandi escarpment north-east of Kisumu and the Mau Forest Complex along its north-eastern border with the Rift Valley Basin from where its major rivers originate, including the Nyando, Sondu, Mara and Gucha rivers. The Mara River crosses the border into Tanzania in the Masai Mara National Reserve. Collectively, these 4 rivers drain almost 80% of the Lake Victoria South Basin. The LVS Basin faces the north-eastern side of Lake Victoria, which is the largest freshwater lake in Africa.
The Lake is a shared water resource between Kenya, Tanzania and Uganda. The main wetlands in the Basin are associated with the Migori, Nyando and Sondu Miriu Rivers originating in the Mau Forest Complex. The Nyando (Kusa) Swamp, located at the mouth of the Nyando River, is covered with dense papyrus beds and is home to many rare bird species. The LVS Basin is one of two basins in Kenya which drains to Lake Victoria. The Lake Victoria Basin is in the upstream part of the Nile River Basin and is shared among five countries.
The total population of the LVS Basin in 2019 was estimated as 8.57 million, which is equivalent to a very high population density of 319 persons/km2 .
Land use in the LVS Basin includes forest, grassland/rangeland and agricultural use. The Basin has a high population density and scattered urban and built-up areas.