This chub is common in an extremely small range (Page and Burr 2011). Estimated population size in Borax Lake ranged from 10,625 to 34,634 during 1991 to 1999; lower Borax Lake, which contained several thousand chubs during wet years in the mid-1980s was dry from 1989 to 1991 and currently (2009) has no fish (U.S. Fish and Wildlife Service; http://www.fws.gov/oregonfwo/Species/Data/BoraxLakeChub/).
The sole habitat consists of a clear, shallow (less than 1 meter deep), 4 ha, alkaline lake (Borax Lake) fed by thermal springs, outflow of the lake, and a pond (Lower Borax Lake) fed by the outflow. Precipitation of minerals from the water over thousands of years has raised the level of the lake approximately 30 feet above the desert playa, isolating the fish from the surrounding watershed.
The springs flowing into the lake have temperatures of about 35-40 °C (95-104 F). The chub prefers water of 29-30 °C (84-86 F); temperatures above 34 °C (93 F) are potentially lethal. The chubs live in those portions of the lake and in the wetlands at the lake's outflow where temperatures are suitable. At temperatures above 30 °C, fishes form loose schools around algae-coated carbonate nodules.
The thermal waters feeding Borax Lake face a long-term threat from geothermal energy development. The small area of available habitat makes the species vulnerable to decreases in water level. Proposals to drill wells near the lake prompted an emergency listing of this species as endangered in 1980. Protection afforded by the Endangered Species Act has greatly curtailed exploratory drilling for geothermal energy development by creation of a zone of no surface disturbance around the most sensitive habitats. The Nature Conservancy, a private conservation organization, purchased a 65-hectare parcel of private land including Borax Lake in 1993. An area of 260 hectares has been designated as critical habitat by the U.S. Fish and Wildlife Service; this affords additional protection from actions by federal agencies. The Steens Mountain Cooperative Management and Protection Act of 2000 (Public Law 106-399) has withdrawn geothermal and mineral development rights from the Borax Lake area. Source: USFWS (2009).
Other threats include modification of the fragile lake shorelines, which easily diverts water away from the lake, and overgrazing by livestock. The perched nature of the lake and its salt-encrusted shoreline render it highly susceptible to damage from off-road vehicle use and human visitation. The area is currently fenced to exclude livestock (USFWS 2009).
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