California
Toxic algae in San Bernardino County lakes
31 lakes and waterways in San Bernardino County have harmful algal bloom reports in California's official data. The most recent entry is for Santa Ana River: There are no bloom reports for Santa Ana River in the last 30 days of California's data. The most recent was an algal mat general awareness sign on 15 September 2026 at Downstream from CA-38 Bridge. Big Bear Lake, Lake Gregory and Horseshoe Lake and 5 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.
- Santa Ana River Awareness sign
- Big Bear Lake Bloom reported
- Lake Gregory Bloom reported
- City Creek Bloom reported
- Horseshoe Lake Bloom reported
- Colorado River Danger
- Lake Havasu Bloom reported
- Spring Valley Lake Bloom reported
- Silverwood Reservoir Bloom reported
- Mill Creek Bloom reported
- Silverwood Lake Bloom reported
- Pelican Lake Bloom reported
- Cucamonga Creek Reach Caution
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.
- Big Bear Lake Ca 2026
- Bill Williams River 2022
- Crab Creek 2026
- Deep Creek 2024
- Grass Valley Lake 2022
- Green Valley Creek 2020
- Green Valley Lake 2023
- Holcomb Creek 2026
- Lake Arrowhead 2022
- Lytle Creek 2024
- Metcalf Creek 2023
- Mid Grout Creek 2023
- Mojave River 2026
- Momyer Creek 2022
- Owl Hole Spring 2024
- Prado Reservoir 2026
- Rathbun Creek 2023
- Santa Ana River Random 2022
Source: California State Water Resources Control Board, official data, checked 24 October 2026. For today's conditions see the California HABs Portal map. No report doesn't mean a lake is safe: most water is only tested occasionally.