The Borax Lake Chub (Siphateles boraxobius) is a small minnow found only in Borax Lake in the Alvord Basin of southeastern Oregon. Borax Lake is fed by geothermal hot springs rich in dissolved minerals and heavy metals that most fish cannot tolerate. Concern over threats to this unique and fragile habitat led to the designation of Borax Lake Chub as Endangered under the federal Endangered Species Act in 1982. Significant actions to protect this habitat included the purchase of the private land containing the lake by The Nature Conservancy, the designation of adjacent public lands as an Area of Critical Environmental Concern, the protection of groundwater and surface water, control of vehicle access to the fragile shoreline, the removal of livestock grazing in the immediate area, and the passage of the Steens Mountain Cooperative Management and Protection Act. Due in large part to these efforts, Borax Lake Chub were removed from the Endangered Species List in 2020.
As part of the delisting decision, a Post-Delisting Monitoring Plan (PDM) was developed by USFWS, ODFW, the BLM, and TNC. The plan includes monitoring population abundance, habitat (in particular, lake elevation, lake temperature, and nonnative species), and geothermal development and exploration in the basin for 10 years following delisting. The Native Fish Investigations Section is responsible for visiting Borax Lake twice annually to evaluate the general health of the local environment, conducting population abundance estimates every three years, and monitoring water temperature and elevation to ensure that Borax Lake Chub continue to thrive.
The most recent population abundance estimate for Borax Lake Chub was completed in October of 2024. NFI estimated the population at approximately 58,633 individuals, modest compared to the 2019 and 2021 estimates, but still slightly above the mean long-term average. Habitat quality remains good, with no evidence of unauthorized vehicle access or other shoreline damage, water levels and temperatures within historic averages, and no evidence of nonnative species in the lake.