Vertical profiles of field fluorometer measurements throughout the water column of Clear Lake, Lake County, California

Clear Lake is a 180 km2 freshwater lake located approximately 120 km northwest of Sacramento in the California Coast Range. The lake is a popular sport-fishing destination, however, there are fish consumption advisories associated with mercury (Hg) contamination for several species. The lake has three arms: a large open-water region to the northwest (Upper Arm), a smaller and narrower region to the southeast (Lower Arm), and the smallest and narrowest region to the east (Oaks Arm). The Sulphur Bank Mercury Mine (SBMM), located on the eastern shore of the Oaks Arm, was mined by underground methods starting in the 1870s and then open-pit methods during the 1920s to 1950s. Since 1990, the SBMM has been a Superfund site managed by the U.S. Environmental Protection Agency. This former Hg mining area is thought to be the dominant contributor of Hg to Clear Lake and is the focus of continued remediation to minimize Hg impacts to Clear Lake. The SBMM area is an active geothermal area with springs and gas fumaroles. Clear Lake is eutrophic to hypereutrophic, based on elevated concentrations of nutrients (various forms of nitrogen, N, and phosphorus, P) that cause excessive algal blooms and periodic fish kills. Monitoring and modeling efforts are being implemented to improve understanding of the ways that nutrient dynamics affect the cycling, transport and bioaccumulation of Hg, which remains poorly understood. This data release documents field-based fluorometer measurements along vertical profiles from June 2023 through May 2025. The fluorometer was attached to a EXO sonde that was taking field measurements along vertical profiles at the same time (Bennett and others, 2026). It includes a data table given as machine readable 'comma-separated values' format (*.csv): 'Clear_Lake_C6P_Profiles', the vertical profile surface-water dataset including the fluorometer measurements.

References:
 
Bennett, P.A., Oldham, N.A., Estrada, C.L., and Alpers, C.N., 2026, Water-Quality Vertical Profiles in Clear Lake, Lake County, California: U.S. Geological Survey data release, https://doi.org/10.5066/P14N6RB3.