The two main sources supply water for the project are Upper Klamath Lake and the Klamath River. The main bodies of water in the Klamath Project are Clear Lake Reservoir, Klamath River, Link River, Lost River, Lower Klamath Lake, Tule Lake, and Upper Klamath Lake. The project fills these reservoirs from the spring runoff, peaking generally in March and April, and keeps the runoff from flooding the historical marshes that are a large portion of the present farmland. There are also many minor streams in the area. Lost River historically drained into Tule Lake, an endorheic lake. The project now diverts excess Lost River water to the Klamath River, allowing portions of Tule Lake to be reclaimed.