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Borax Lake Chub

Photo of a Borax Lake chub by the USFWS

Scientific name: Gila boraxobius 

Status: Delisted due to recovery

Critical Habitat: Designated

Listing Activity: The Borax Lake chub was emergency-listed as endangered in 1980, and a final listing rule with critical habitat (47 FR 43957) was published in 1982. A recovery plan was published in 1987. On February 26, 2019, the USFWS published a proposal to remove the Borax Lake chub, and its critical habitat, from the list of Endangered and Threatened Species in the federal register.

Potential Range Map

  • Description and Life History

    The Borax Lake chub is a dwarf species of the genus Siphateles (a widespread desert minnow formerly classified under the genera Gila). Adults are typically 33 to 50 millimeters (1.3 to 2 inches) standard length, with a maximum recorded size of 93 millimeters (3.6 inches) standard length. The Borax Lake chub has a large head which is concave in profile. The eyes are large, and the lateral line is reduced. Pharyngeal teeth are uniserial and well-hooked. The Borax Lake chub is an opportunistic omnivore, feeding on aquatic and terrestrial insects, algae, mollusks and mollusk eggs, aquatic worms, spiders, and seeds.  Borax Lake chub prefer the shallow habitats along the margins of the lake. Males and females can reach reproductive maturity within one year.  Spawning can occur year-round, but primarily takes place in the fall and spring. Spawning occurs primarily in gravel, rock outcrop, and sand habitats, which comprise only 16 percent of the substrate of Borax Lake.

    Population abundance estimates for the Borax Lake chub were conducted annually from 1986 to 1997, from 2005 to 2012, and from 2015 to 2017.  Over this period, the population abundance has shown a high degree of variability, ranging from a low of 1,242 in 2015, to a record high of 76,931 in 2017. A pattern of population reduction followed by a 1- to 5-year period of rebuilding has been observed multiple times during the period of record. The mechanisms contributing to variability in abundance are not entirely clear, but water temperatures some years exceed the suspected thermal critical maximum. Survival and recruitment are likely higher during years when water temperatures are cooler in the lake. Water temperatures in Borax Lake are driven by a deep geothermal aquifer. Water temperature is also influenced by a variety of other factors, including air temperature, inflow from smaller geothermal and cool water springs, ephemeral thermoclines between areas of relatively cooler and warmer water, and wind. 


    Borax Lake, with its highly variable geothermal springs, comprises one of the most unusual fish habitats in the United States. Borax Lake is a natural lake fed from the waters of several geothermal springs, and is perched 10 meters (30 feet) atop large sodium-borate deposits in the Alvord Desert. It is small and shallow, about 4.1 hectares (10 acres) in size. A 0.5 m (1.6 ft) thick flocculent silt covers the lake bottom, with patches of bedrock, fine gravel, and sparse growth of aquatic plants.  Spring inputs near the bottom of a deep vent, 32 meters (100 feet) below the surface, range from 40 to 148°C (104 to 298°F). Surface water temperatures typically range from 16 to 38°C (61 to 100°F), and are variable throughout the lake.  Water flows from Borax Lake into surrounding marshes and small pools.

    The only habitat outside of Borax Lake that provides habitat for Borax Lake chub is the “marsh” or “wetland”, the overflow channel that connects the wetland to Borax Lake, and a second overflow channel on the northern end of the lake.  Although the wetland at times maintains water year-round, water levels are variable and are influenced by a groundwater vent in the wetland and overflow from Borax Lake.  The seasonal pattern and overall contribution of groundwater inputs to the wetland are dynamic and not understood.  These wetlands may provide refuge for during periods of high water temperature in Borax Lake.

    Reasons for Decline

    The Borax Lake chub was not listed due to a decline in abundance or distribution. Federal protections were directed at threats to the species’ habitat. Proposal and investigations to develop geothermal energy from the thermal water aquifer supporting Borax Lake were initiated in the 1970s. Proposals to drill wells near the lake prompted an emergency listing of this species as endangered in 1980. Other threats include modification of the fragile lake shorelines, which easily diverts water away from the lake, and overgrazing by livestock. The fragile salt-crust shoreline of the lake also is easily damaged by off-road vehicle use.

    Conservation Measures

    In 1987, the U.S. Fish and Wildlife Service published a recovery plan for the Borax Lake chub.  The goal of this plan was to ensure the long term protection of the species and its habitat.  The plan outlined the recovery objectives for the species, and called for monitoring the health and viability of the population, monitoring for nonnative species, protection of the geothermal water that feeds Borax Lake, construction and maintenance of fencing around the lake to exclude livestock and off-road vehicles.

    A number of regulatory actions have occurred that provide long term protection for Borax Lake chub.  ODFW filed for and obtained water rights in 1991 to ensure maintenance of the water elevation at Borax Lake. The Nature Conservancy purchased a 160 ha (65 ac) parcel of private land containing Borax Lake and subsurface mineral rights in 1993.  The Bureau of Land Management designated a 243 ha (600 ac) parcel of adjacent public lands as an Area of Critical Environmental Concern. BLM and TNC fenced the area to exclude livestock and off-road vehicles.  The passage of the Steens Mountain Act in 2000 and the BLM Resource Management Plan withdrew mineral and geothermal resource development within the Alvord Known Geothermal Resource Area.

    The Borax Lake chub is a conservation-reliant species, which requires continued active management to sustain the species and its habitat. In 2018, a Conservation Management Plan was prepared and signed by BLM, ODFW, and USFWS to guide future management, conservation, and protection of the Borax Lake chub, regardless of listing status. Along with the proposal to delist the species, the USFWS made a draft post-delisting monitoring plan available for public comment.  The post-delisting monitoring plan builds upon and continues the research, monitoring, and management that took place while the species was listed, to ensure the species remains secure without the protections of the Endangered Species Act.  The PDM outlines regular monitoring to ensure conservation thresholds are met over a 10 year period following delisting.

    Due to the successful implementation of the recovery plan, the species' recovery objectives were met, and threats to the species largely ameliorated. On February 26, 2019, the USFWS published a proposed rule in the federal register to remove the Borax Lake chub, and its critical habitat, from the list of Endangered and Threatened Species (delist) due to recovery.


    U.S. Fish and Wildlife Service.  2019.  Proposed Rule: Removing the Borax Lake Chub From the Federal List of Endangered and Threatened Wildlife. FR (84):6110-6127.

    U.S. Fish and Wildlife Service. 1987. Recovery plan for the Borax Lake chub, Gila boraxobius. U.S. Fish and Wildlife Service, Portland, Oregon. 61 pp.

    Williams, J. E. & C. E. Bond. 1983. Status and life history notes on the native fishes of the Alvord Basin, Oregon and Nevada. Great Basin Naturalist. 43:409-420.

    Williams, J. E. & C.D. Williams. 1980. Feeding ecology of Gila boraxobius (Osteichthyes: Cyprinidae) endemic to a thermal lake in southeastern Oregon. Great Basin Naturalist. 40:101-114.

    Williams, J.E. 1995. Threatened fishes of the world: Gila boraxobius Williams and Bond, 1980 (Cyprinidae). Environmental Biology of Fishes 43: 294.


    Last updated: February 25, 2020

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