Geochemical data for selected streams in the Clear Lake basin, Lake County, California (ver. 2.0, March 2026)

This dataset includes water-quality data collected at 16 sites in the Clear Lake Drainage Basin, Lake County, California, between November 2018 and March 2025. Sampling targeted high-flow events following rainfall and baseline conditions during the wet season (typically December through April) across multiple water years (WYs), with expanded coverage in WYs 2022–2024 and new data added for WY 2025. Sampling sites span several tributaries, including Scotts Creek, South Fork Scotts Creek, Middle Creek, Adobe Creek, Clover Creek, Cole Creek, and Kelsey Creek. Sampling periods varied by site, with some locations sampled intermittently between WYs 2019 and 2025. Sampling in the reach of the Scotts Creek drainage below the confluence with South Fork Scotts Creek (USGS stations 11448800 and 390236122575901) was done during November 2018 to May 2019, WY 2019 and also during WYs 2021-24. Sampling at South Fork Scotts Creek near Lakeport (11448750) and Scotts Creek at Eickhoff Road Bridge near Lakeport (390544122574201) was done during WYs 2021-24. Sites on several creeks in the basin were sampled during WYs 2022-24: Clover Creek Bypass at Elk Mountain Road (11449235), Cole Creek at Kelseyville (11449820), Kelsey Creek near Kelseyville (11449500), Kelsey Creek above Soda Bay Road near Kelseyville (390030122502101), and Middle Creek at Rancheria Road (391057122544301). Two sites on Middle Creek were sampled only during WYs 2022-23: Middle Creek Near Vann (391448122565601) and Middle Creek below Elk Mountain Road near Upper Lake (391227122553101). Two sites on Adobe Creek (390054122521501 and 390054122532801) were sampled only during WY 2023. Two sites on Scotts Creek below Tule Lake (11390936122551901 and 11449255) were sampled during WY2021 and WYs 2023-24, respectively, and a site on Molesworth Creek (11449370) was sampled during WYs 2023-24. Two analytical schedules were used:

Schedule A (116 samples at 6 sites): Included total and methylmercury (filtered and particulate), dissolved organic carbon (DOC), optical properties, nutrients (nitrogen and phosphorus), and total suspended sediment (TSS).

Schedule B (148 samples at 10 sites): Included similar parameters but excluded mercury species, DOC, and optical properties.

In Version 2.0, additional data collected between December 2023 and March 2025 were added, including:
Field measurements (Table 03_CLT_WQ_Field.csv )
Particle size distribution results (Table 04_CLT_WQ_SS.csv)
Nutrient concentrations (Table 05_CLT_WQ_Nutrients.csv)
Filtered and particulate mercury concentrations (Tables 06_CLT_WQ_Mercury.csv and 14_CLT_QC_Mercury.csv)
Anion concentrations (Table 08_CLT_WQ_Anions.csv)
QA/QC summaries for mercury data (Table 10_CLT_WQ_QA_Mercury.csv)
Selected samples were also analyzed for stable isotopes of nitrogen and oxygen in dissolved nitrate (WYs 2022–2023), and for median and mean grain size of suspended sediment.
These data support ongoing efforts to understand sediment and nutrient transport, mercury cycling, and water-quality dynamics in the Clear Lake watershed.

Version History Summary:
First Published: April 2025
Version 2.0: March 13, 2026