Lake by lake, from official state data
Oregon algae blooms
Oregon has recorded harmful algal blooms at 69 lakes and rivers since 2010. The latest published data runs to 23 December 2025, and 20 lakes have had blooms in three or more years.
Open the Oregon algae bloom map
Latest reports in Oregon
The most recent entries in Oregon's published data. For this season, check the OHA current advisories page.
- Upper Klamath Lake Health advisory
- Gerber Reservoir Precaution
- Thief Valley Reservoir Health advisory
- Brownlee Reservoir Health advisory
- Tenmile Lakes Precaution
- Wapato Marsh Health advisory
- Hells Canyon Reservoir Health advisory
- Devils Lake Precaution
- Eckman Lake Health advisory
- Willamette River Precaution
- Haystack Reservoir Precaution
- Cullaby Lake Precaution
Lakes with the most bloom years
Lakes where toxic algae comes back year after year.
| Lake | County | Years with blooms |
|---|---|---|
| Willow Creek Reservoir | Morrow | 12 |
| Upper Klamath Lake | Klamath | 10 |
| South Umpqua River | Douglas | 10 |
| Willamette River | Multnomah | 8 |
| Lake Billy Chinook | Jefferson | 7 |
| Tenmile Lakes | Coos | 7 |
| Odell Lake | Klamath | 7 |
| Lost Creek Lake | Jackson | 6 |
| Brownlee Reservoir | Baker | 6 |
| Cullaby Lake | Clatsop | 6 |
| Dorena Reservoir | Lane | 5 |
| Hells Canyon Reservoir | Baker | 5 |
| Blue Lake | Multnomah | 4 |
| Detroit Lake | Linn | 4 |
| Devils Lake | Lincoln | 4 |
Oregon counties
Every county with at least one lake or river in the state's bloom records.
How Oregon tracks toxic algae
The Oregon Health Authority (OHA) collects bloom reports from its own staff, local agencies and the public. Its data is published as a yearly advisory archive; this season's advisories are on the OHA advisories page. This site groups those reports by lake so you can see each lake's latest entry and its full history in one place.
Not every lake is tested, and lakes that are tested are usually checked only some of the time. A lake with no report may simply not have been looked at, so always follow posted signs and avoid green, scummy or discoloured water. View the source data.