Mann Lake is the largest of the shallow playa lakes in the northern part of the Alvord Valley in

Harney County Harney County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 7,495, making it the sixth-least populous county in Oregon. The county seat is Burns. Established in 1889, the county is named in h ...

in the U.S. state of

Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idaho. T ...

. The lake is a remnant of a larger

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

lake that covered much of the valley, east of

Steens Mountain Steens Mountain is in the southeastern part of the U.S. state of Oregon, and is a large fault-block mountain. Located in Harney County, it stretches some north to south, and rises from the west side the Alvord Desert at elevation of about t ...

. Fields–Denio Road runs along the east side of the lake. Inflow to Mann Lake comes from small, intermittent streams, mainly from Steens Mountain. The lake, which has no outlet, but loses water by evaporation, is

hypereutrophic The Trophic State Index (TSI) is a classification system designed to rate water bodies based on the amount of biological productivity they sustain. Although the term "trophic index" is commonly applied to lakes, any surface water body may be inde ...

. An influx of cattle waste from nearby rangelands adds to the lake's natural eutrophic state. Large concentrations of''

Cladophora ''Cladophora'' is a genus of reticulated filamentous Ulvophyceae (green algae). The genus ''Cladophora'' contains many species that are very hard to tell apart and classify, mainly because of the great variation in their appearances, which is a ...

'' algae are common. The Bureau of Land Management operates the Mann Lake Recreation Site, about southeast of

Burns Burns may refer to: * Burn, an injury (plural) People: * Burns (surname), includes list of people and characters Business: * Burns London, a British guitar maker Places: ;In the United States * Burns, Colorado, unincorporated community in Eagle ...

by highway and unpaved road. The site has vault restrooms and boat ramps, but no other amenities. Recreation at or near the site includes fishing, camping, hiking, wildlife viewing, and

amateur geology Amateur geology or rock collecting (also referred to as rockhounding in the United States and Canada) is the non-professional study and hobby of collecting rocks and minerals or fossil specimens from the natural environment.Sinkankas, John. Minera ...

. Mann Lake, stocked with

Lahontan cutthroat trout Lahontan cutthroat trout (''Oncorhynchus clarkii henshawi'') is the largest subspecies of cutthroat trout, and the state fish of Nevada. It is one of three subspecies of cutthroat trout that are listed as federally threatened. Natural history ...

, has been called "one of the premiere trout fisheries in southeast Oregon". Trout in the lake range in length from . Fishing is restricted to artificial flies and lures. A large population of

goldfish The goldfish (''Carassius auratus'') is a freshwater fish in the family Cyprinidae of order Cypriniformes. It is commonly kept as a pet in indoor aquariums, and is one of the most popular aquarium fish. Goldfish released into the wild have bec ...

, introduced illegally, have at times multiplied in Mann Lake and competed for food with the smaller trout. In 2010, the

Oregon Department of Fish and Wildlife The Oregon Department of Fish and Wildlife (ODFW) is a government agency of the U.S. state of Oregon responsible for programs protecting Oregon fish and wildlife resources and their habitats. The agency operates hatcheries, issues hunting an ...

treated the lake with

rotenone Rotenone is an odorless, colorless, crystalline isoflavone used as a broad-spectrum insecticide, piscicide, and pesticide. It occurs naturally in the seeds and stems of several plants, such as the jicama vine plant, and the roots of several mem ...

, a

piscicide A piscicide is a chemical substance which is poisonous to fish. The primary use for piscicides is to eliminate a dominant species of fish in a body of water, as the first step in attempting to populate the body of water with a different fish. They ...

, killing around 200,000 goldfish and

fathead minnow Fathead minnow (''Pimephales promelas''), also known as fathead or tuffy, is a species of temperate freshwater fish belonging to the genus ''Pimephales'' of the cyprinid family. The natural geographic range extends throughout much of North Amer ...

s while sparing nearly all the trout.

References

External links

*
Mann Lake Campground
– Public Lands Information Center {{authority control Lakes of Oregon Lakes of Harney County, Oregon Endorheic lakes of Oregon

See also

References

External links