UC Davis report identifies Cole Creek as nutrient hotspot with volatile flows

UC Davis published its Clear Lake Watershed and Lake Remediation Final Report in January 2026 with several findings specific to Cole Creek.

Cole Creek has the second-highest ratio of bioavailable phosphorus (37%) of all sampled tributaries, and 17% of its sediment phosphorus is in the Iron-Aluminum form most likely to release into the water when oxygen drops. These samples were collected at the USGS gage in Kelseyville, upstream of the flood-prone lower reach. When we asked the research team about this, they confirmed that "the specific impact of long-term standing water on the lower floodplain was not a distinct variable isolated in the current nutrient export calculations." The actual load reaching Clear Lake could be higher.

Cole Creek's annual discharge more than doubled from roughly 4.4 million cubic meters in Water Year 2023 to 9.4 million cubic meters in Water Year 2024. The report describes these tributaries as "storm-driven flashy creeks experiencing high interannual hydrological variability."

The report found that Cole Creek delivered only 1.5% of the total sediment load to the lake despite covering about 23% of the modeled watershed area. The research team confirmed this measures the "delivered load," which "may indeed be lower than the 'total mobilized sediment' precisely because of the settling behavior" in the lower reaches. This matches the chronic channel blockages we have been documenting: sediment gets trapped, fills the creek bed, and worsens flooding instead of washing through.