Klamath Lake

Upper Klamath Lake
Aerial view of Williamson River and Agency Lake
Location	Klamath County, Oregon, United States
Coordinates	42°23′32″N 121°52′49″W / 42.39222°N 121.88028°W / 42.39222; -121.88028Coordinates: 42°23′32″N 121°52′49″W / 42.39222°N 121.88028°W / 42.39222; -121.88028
Lake type	Hypereutrophic
Primary inflows	Williamson River, Wood River, Crooked Creek, Fourmile Creek
Primary outflows	Link River
Catchment area	3,768 sq mi (9,760 km2)
Basin countries	United States
Max. length	20 mi (32 km)
Max. width	8 mi (13 km)
Surface area	61,543 acres (24,906 ha)
Average depth	14 ft (4.3 m)
Water volume	849,290 acre·ft (1.04758 km3)
Residence time	0.5 months
Shore length1	87.8 mi (141.3 km)
Surface elevation	4,140 feet (1,260 m)
1 Shore length is not a well-defined measure.

Upper Klamath Lake (sometimes called Klamath Lake) (Klamath: ?ews, "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).

In the early 20th century, most of the wetlands and marshes surrounding the lake were drained for agricultural purposes, damaging the larger habitat. The lake's water has been used to support the federal Klamath Project for irrigation by local farmers for a century. The lake depth fluctuates due to regulation of its water supply, averaging between 8 to 50 feet (2.4 to 15.2 m) deep. The lake level is kept within 4,137 to 4,143 ft (1,261 to 1,263 m) above sea level to ensure a viable fishery in the lake and to protect coho salmon in the Klamath River below the lake.

Upper Klamath Lake is fed by a watershed of 3,768 square miles (9,760 km²) including the Williamson and Wood Rivers, and is drained by the Klamath River (known here as the Link River), which issues from the south end of the lake. The lake is connected by a short channel to the smaller Agency Lake to the north. The Upper Klamath National Wildlife Refuge has been established on land along the northern edge of the lake to preserve natural habitat.

Upper Klamath Lake is the largest remnant of Lake Modoc, a giant pluvial lake that existed in the region until about 10,000 years ago. At its largest, Lake Modoc covered over 1,000 square miles (2,600 km²), joining Upper Klamath, Lower Klamath, and Tule Lakes, as well as all of the major wetlands in the upper Klamath River basin, into a contiguous body of water. The lake was more than ten times the size of present-day Upper Klamath Lake and sat nearly 100 feet (30 m) higher in elevation. Lake Modoc disappeared at the end of the due to a warming and drying climate.