Oregon
Toxic algae in Klamath County lakes
9 lakes and waterways in Klamath County have harmful algal bloom reports in Oregon's official data. The most recent entry is for Upper Klamath Lake: Oregon issued a health advisory for Upper Klamath Lake in 2025, listed on 23 December 2025. Upper Klamath Lake, Gerber Reservoir and Odell Lake and 1 more have had blooms in three or more years.
Lakes with bloom history
Newest report first. Each lake has its own page with the full history and what the results mean.
Other waterbodies with a report
These have one or two reports in a single year, which isn't enough history for a page of their own yet.
- JC Boyle Reservoir 2021
- Keno Reservoir 2018
- Klamath River 2017
- Lake Ewauna 2023
- Smith Reservoir 2025
Source: Oregon Health Authority (OHA), official data, checked 24 October 2026. For today's conditions see the OHA current advisories page. No report doesn't mean a lake is safe: most water is only tested occasionally.