Upper Klamath Lake (sometimes called Klamath Lake) is a large, shallow freshwater lake east of the Cascade Range in south-central Oregon in the United States. The largest body of fresh water by surface area in Oregon, it is approximately 25 miles (40 km) long and 8 miles (13 km) wide and extends northwest from the city of Klamath Falls. It sits at an average elevation of 4,140 feet (1,260 m).

Being naturally stagnant, the lake has been known since early times for its poor water quality. Frémont noted the "often foul smelling waters" of the lake, and the Applegate Trail was purposely routed away from the lake because the water was "so bad that it might be too dangerous for livestock to drink late in the season".

The algae blooms turn the water an opaque green in the summer and reduce the opportunity for recreational uses of the lake. State standards for dissolved oxygen are routinely violated, meaning that fish are endangered. The lake is still a vital stop for waterfowl along the Pacific Flyway, and is known for its rainbow trout fishery.

The future uses of Klamath Lake are of national interest because of competing claims between farmers' property rights (supported by federal subsidies and programs) and larger environmental goals.

More Info: en.m.wikipedia.org