Lake Naivasha is a freshwater lake in Kenya, outside the town of Naivasha in Nakuru County, which lies North West of Nairobi. It is part of the Great Rift Valley. The name derives from the local Maasai name Nai'posha, meaning "rough water" because of the sudden storms which can arise.

Lake Naivasha is at the highest elevation of the Kenyan Rift valley at 1,884 meters (6,181 ft.) in a complex geological combination of volcanic rocks and sedimentary deposits from a larger Pleistocene Era lake. Apart from transient streams, the lake is fed by the perennial Malewa and Gilgil rivers. There is no visible outlet, but since the lake water is relatively fresh, it is assumed to have an underground outflow.

The lake has a surface area of 139 square kilometers (54 sq. mi), and is surrounded by a swamp that covers an area of 64 square kilometers (25 sq. mi), but this can vary largely depending on rainfall. It is situated at an altitude of 1,884 meters (6,181 ft.).The lake has an average depth of 6 meters (20 ft.), with the deepest area being at Crescent Island, at a maximum depth of 30 meters (98 ft.). Njorowa Gorge once formed the lake's outlet, but it is now high above the lake and forms the entrance to Hell's Gate National Park. The town of Naivasha (formerly East Nakuru) lies on the north-east edge of the lake.