California lakes: toxic algae status
Harmful algal bloom (blue-green algae) reports for California lakes and rivers, from the California State Water Resources Control Board.
Data updated daily. Latest entry: 19 October 2026. For today's conditions, see the California HABs Portal map.
879
waterbodies with a bloom report (2015–2026)
318
lakes with enough history for a full page
168
lakes with blooms in 3 or more different years
Lakes with the most bloom years
| Lake | County | Years with blooms |
|---|---|---|
| Clear Lake | Lake | 11 |
| Lake Isabella | Kern | 11 |
| Discovery Bay | Contra Costa | 11 |
| Lake Oroville | Butte | 10 |
| Pyramid Lake | Los Angeles | 9 |
| Tahoe Keys Lagoon | El Dorado | 9 |
| San Luis Reservoir | Merced | 9 |
| Lake Chabot | Alameda | 9 |
| Pinto Lake | Santa Cruz | 9 |
| Lake Temescal | Alameda | 9 |
| Russian River | Sonoma | 8 |
| Salton Sea | Imperial | 8 |
| Lake Tahoe | El Dorado | 8 |
| South Fork Eel River | Humboldt | 8 |
| Eagle Lake | Lassen | 8 |
Browse by county
- Alameda County (23 waterbodies)
- Alpine County (19 waterbodies)
- Butte County (12 waterbodies)
- Calaveras County (10 waterbodies)
- Colusa County (3 waterbodies)
- Contra Costa County (20 waterbodies)
- Del Norte County (7 waterbodies)
- El Dorado County (27 waterbodies)
- Fresno County (9 waterbodies)
- Glenn County (3 waterbodies)
- Humboldt County (24 waterbodies)
- Imperial County (6 waterbodies)
- Inyo County (11 waterbodies)
- Kern County (12 waterbodies)
- Lake County (23 waterbodies)
- Lassen County (9 waterbodies)
- Los Angeles County (34 waterbodies)
- Madera County (17 waterbodies)
- Marin County (18 waterbodies)
- Mariposa County (8 waterbodies)
- Mendocino County (17 waterbodies)
- Merced County (3 waterbodies)
- Modoc County (9 waterbodies)
- Mono County (27 waterbodies)
- Monterey County (23 waterbodies)
- Napa County (9 waterbodies)
- Nevada County (24 waterbodies)
- Orange County (16 waterbodies)
- Placer County (16 waterbodies)
- Plumas County (27 waterbodies)
- Riverside County (32 waterbodies)
- Sacramento County (31 waterbodies)
- San Bernardino County (31 waterbodies)
- San Diego County (60 waterbodies)
- San Francisco County (4 waterbodies)
- San Joaquin County (21 waterbodies)
- San Luis Obispo County (15 waterbodies)
- San Mateo County (15 waterbodies)
- Santa Barbara County (8 waterbodies)
- Santa Clara County (13 waterbodies)
- Santa Cruz County (13 waterbodies)
- Shasta County (15 waterbodies)
- Sierra County (9 waterbodies)
- Siskiyou County (28 waterbodies)
- Solano County (6 waterbodies)
- Sonoma County (21 waterbodies)
- Tehama County (7 waterbodies)
- Trinity County (22 waterbodies)
- Tulare County (19 waterbodies)
- Tuolumne County (11 waterbodies)
- Ventura County (9 waterbodies)
- Yolo County (8 waterbodies)
- Yuba County (9 waterbodies)
Source: California State Water Resources Control Board, official data. This site is independent and not affiliated with the State of California.