Is Heenan Reservoir safe? Toxic algae status
Alpine 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.
6
bloom reports since 2020
4 of 4
years with a bloom reported (2020–2023)
2
advisories recommended: 2 Caution, 0 Warning, 0 Danger
Year by year
Each box shows bloom reports logged that year, coloured by the highest advisory recommended.
Reports at Heenan Reservoir are most often logged in May, June and August.
Recent reports
| Date | Location | Result |
|---|---|---|
| 19 August 2023 | Dam | Bloom reported |
| 23 June 2023 | Loading Zone | Bloom reported |
| 24 August 2022 | Dam | Caution |
| 11 May 2022 | Loading Zone | Caution |
| 17 May 2021 | Heenan Reservoir | Bloom reported |
| 20 October 2020 | Heenan Lake | Bloom reported |
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 Heenan Reservoir safe to swim in?
The most recent entry in California's published data is from 19 August 2023: bloom reported (Dam). Blooms have been recorded at Heenan Reservoir in 4 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 Heenan Reservoir get algae blooms?
In the state's records, reports are most often logged in May, June 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. This page is independent and not affiliated with the State of California.