Hot Creek Nitrogen Site-Specific Objectives Update

Background

Hot Creek is located east of Hwy 395 near Mammoth Lakes and is tributary to the Owens River. Hot Creek begins just downstream of Hwy 395 and flow is dominated by Mammoth Creek from Substation Road until the confluence with outflow from the Hot Creek Hatchery. For the purpose of this project, Hot Creek begins where the hatchery outflow joins the main stem of Hot Creek. The water supply to Hot Creek Hatchery originates from several geothermally influenced springs. Nitrogen concentrations in the springs that supply the Hatchery, in the Hatchery effluent, and in the receiving water downstream of the Hatchery regularly exceed the total nitrogen (TN) water quality objectives for Hot Creek and, at times, exceed the nitrate objective.

Past studies to assess conditions in Hot Creek generally conclude that the nitrogen originating from the springs are leading to potentially eutrophic conditions including abundant aquatic vegetation in both the springs upstream of the raceways and in Hot Creek downstream of the Hatchery. Secondary impacts to Hot Creek are attributed to Hatchery operations that result in the discharge of organic matter and TN. It is likely a combination of factors, including high nutrient levels and stream temperatures which influence downstream vegetation. Other sources of nitrogen to Hot Creek are currently being investigated.

Project Description

This project would consider modifying the TN and nitrate site-specific water quality objectives (WQO) for Hot Creek. The Hot Creek WQO for TN (0.3 mg/L, Annual Average; 1.5 mg/L 90th percentile) is routinely exceeded and the nitrate WQO (0.2 mg/L, Annual Average; 0.4 mg/L 90th percentile) is occasionally exceeded.

During the 2022 Triennial Review of the Lahontan Regional Water Quality Control Plan (Basin Plan), the Board prioritized creation of an updated TN WQO for Hot Creek. This commitment was reaffirmed in the 2025 Triennial Review. Since being prioritized in the 2022 Triennial Review, basin planning staff began investigations in support of a possible Basin Plan amendment. This includes obtaining data through field work and by requests to CDFW hatchery staff. One consideration for this Basin Plan amendment is that water in the springs, from which the hatchery raceways are fed, fails to meet the Hot Creek nitrogen WQOs. The source of this nitrogen is not fully characterized and may be naturally occurring or influenced by upgradient nitrogen inputs to groundwaters. Another factor to consider is that the location from where the current nitrogen WQOs apply is downstream of the Hot Creek Geologic Site, where boiling water bubbling up from the creek bed, fumaroles and periodic geyser eruptions occur, complicating the water chemistry. For these reasons, basin planning staff are coordinating with multiple regulatory programs to update Hot Creek WQOs for nitrogen.

Project Announcements and Documents

• Fact Sheet