Luis Santana, chair of the Lake County Fish and Wildlife Advisory Committee and fish and wildlife director for Danoha Fish and Wildlife for Robinson Rancheria, told the board the fish kill occurred in the first two weeks of September and that field measurements point to a low dissolved-oxygen event.

“I took a shoreline sample and the Dissolved Oxygen was bad, but it wasn't too bad. It's definitely something that fish could live in,” Santana said, describing an initial shoreline reading of about 3.95 milligrams per liter in Soda Bay. He said he followed up the next day with vertical profiles and found far lower values across the water column at multiple sites.

Santana reported mid-lake profiles with extremely low oxygen: about 0.52 mg/L at roughly 3 feet below the surface, 0.28 mg/L at 17 feet and 0.22 mg/L at 30 feet. He said Dorn Bay readings included about 1.2 mg/L near the surface, about 1.0 mg/L at 7 feet and 0.2 mg/L at 13 feet; Keeling-area profiles showed roughly 0.9 mg/L at 2 feet, 0.3 mg/L at 14 feet and 0.2 mg/L near 29 feet. He said those values render the water column “not suitable for fishes in those areas.”

Santana listed species observed dead or affected at shorelines and in sampling: Clear Lake hitch and other cyprinids; Sacramento sucker; Sacramento blackfish; threadfin shad; largemouth bass; black crappie; and bluegill. He noted channel catfish and bullhead, which tolerate lower oxygen, were still present.

The advisory committee also recovered a large white sturgeon and took the head and pectoral fins for laboratory analysis. Santana said the fish was a large female, about 7 feet 7 inches, and that tissue samples had been sent to a lab; he said staff expect more information in the coming weeks. He characterized the overall evidence as a low dissolved-oxygen event.

County water-resources staff corroborated the advisory-committee findings. “We did vertical profiles on the lake on September 10, which I believe was 3 days after Luis gathered his data with our monthly water quality,” said Chris Childers, Water Resources Department program coordinator. “We found the same thing that he's seeing here. So very, very low dissolved oxygen from the surface all the way down to the bottom in all 3 arms of the lake.”

Board members and public commenters asked about causes and whether planned restoration work or a proposed hypolimnetic oxygenation project could prevent future events. Santana said decomposition of algae can cause oxygen loss in some years, but that the data for this event did not indicate a cyanobacteria die-off; he characterized this occurrence as more consistent with a late-season turnover event and cited a UC Davis measurement that had predicted a low dissolved-oxygen occurrence.

Angela, executive director of the Lake County Land Trust, provided broader context for seasonal variability. Drawing on past local patterns she described, she said drought years followed by high-water years can create conditions for increased aquatic growth and later die-off, which in turn can consume oxygen and produce periodic fall fish kills.

On the question of mitigation, Santana said localized restoration and oxygenation projects could provide refuge in specific areas but would not necessarily protect fish across the entire lake during a widespread low-oxygen or turnover event.

Santana said he is finishing a written report with mapped sampling locations, GPS coordinates and tables and will distribute it to the board. Laboratory results from the sturgeon specimens are expected in the coming weeks and staff said they will continue monitoring and coordinating sampling.

No formal motion or vote was recorded on this agenda item.