Lake Chala,

Lake Chala, also known as Lake Challa, is a crater lake that straddles the border between Kenya and Tanzania. The lake formed approximately 250,000 years ago. The lake is east of Mount Kilimanjaro, 8 kilometres (5.0 mi) north of Taveta, Kenya, and 55 kilometres (34 mi) east of Rombo District. The lake is surrounded by a steep crater rim with a maximum height of 170 metres (560 ft). Lake Chala's average annual rainfall is about 565 millimetres (22.2 in). The lake surface has an average annual evaporation of near 1,735 millimetres (68.3 in). Approximately 80 percent of the lake's inflow comes from groundwater, which is derived mostly from rainfall in the montane forest zone of Mount Kilimanjaro at an elevation of 1,800 to 2,800 metres (5,900 to 9,200 ft). It takes about 3 months for groundwater to reach the lake. The groundwater flowed into the lake at an estimated annual volume of 8,390,000 cubic metres (296,000,000 cu ft) from 1964 through 1977.