Is Trinity River safe? Toxic algae status
Trinity County, California. Harmful algal bloom (blue-green algae) reports from the California State Water Resources Control Board.
Data checked 24 October 2026. California data is updated daily.
35
bloom reports since 2018
7 of 9
years with a bloom reported (2018–2026)
3
advisories recommended: 3 Caution, 0 Warning, 0 Danger
Year by year
Each box shows bloom reports logged that year, coloured by the highest advisory recommended.
Reports at Trinity River are most often logged in January, July and August.
Recent reports
| Date | Location | Result |
|---|---|---|
| 19 August 2026 | Tish Tang Campground River access | Bloom reported |
| 5 August 2024 | South Bend (off road just north of Willow Creek) | Bloom reported |
| 24 August 2023 | Lagoon connected to river near Rush Creek Rd. | Bloom reported |
| 21 June 2023 | at Weitchpec | Bloom reported |
| 23 January 2023 | at the Southern Boundary of Reservation | Bloom reported |
| 7 January 2022 | at the Southern Boundary of Reservation | Bloom reported |
| 4 August 2021 | near Klamath River | Bloom reported |
| 31 July 2021 | at Big Rock | Bloom reported |
| 27 July 2021 | near Sheridan Creek | Algal mat alert sign |
| 27 July 2021 | near Francis B. Matthews Rest Area | Algal mat alert sign |
| 27 July 2021 | near Trinity Village | Algal mat alert sign |
| 27 July 2021 | near Cedar Flat | Algal mat alert sign |
What the results mean
Algae may be present. Stay away from scum and discoloured water, and keep pets and livestock from drinking it.
Toxins at higher levels. No swimming, and keep pets and children well away from the water.
High toxin levels. Stay out of the water and off the shoreline.
Dogs and toxic algae
Dogs face the greatest risk because they swallow water and lick algae off their fur. If a bloom has been reported, keep dogs out of the water and away from scum on the shore. If your dog swims in water that might have algae, rinse it with clean water straight away and call a vet if it seems unwell.
Common questions
Is Trinity River safe to swim in?
The most recent entry in California's published data is from 19 August 2026: bloom reported (Tish Tang Campground River access). Blooms have been recorded at Trinity River in 7 different years, so treat green, scummy or discoloured water with caution. For current conditions, check the California HABs Portal map and posted signs.
When does Trinity River get algae blooms?
In the state's records, reports are most often logged in January, July and August. Blooms are most likely in warm, calm weather, but they can appear at other times of year.
Source: California State Water Resources Control Board, official data. Trinity River spans Humboldt County and Trinity County; reports from all of them are combined here. This page is independent and not affiliated with the State of California.