Mountain Meadows Reservoir: toxic algae advisories
Mountain Meadows Reservoir, Lassen County. See all Lassen County waters.
What the state's records say
Caution advisory, last posted Aug 11, 2026. No all-clear recorded.
4 reported spots here have an advisory with no all-clear recorded.
Reporting is voluntary, so the state may not have recorded an end even if conditions changed. Check posted signs and the official map.
What this level asks: Algae that can make toxins may be present. Keep people, children and pets away from algae and scum, and do not let pets drink the water.
Before you go, check the state's official algae page and any signs posted at the water.
Dogs at Mountain Meadows Reservoir
The state has an advisory on file for Mountain Meadows Reservoir (Caution advisory), last posted Aug 11, 2026, and no all-clear recorded. Keep your dog out of the water and away from scum on the shore until the state records an end.
Satellite estimate (not an advisory)
Week ending Jun 27, 2026: about 7,200 cells/mL of cyanobacteria near the center of Mountain Meadows Reservoir.
A satellite estimate from EPA CyAN for a 19.6 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Jun 27, 2026 | about 7,200 cells/mL |
| Jun 13, 2026 | about 8,100 cells/mL |
| Oct 11, 2025 | about 82,000 cells/mL |
| Sep 13, 2025 | about 37,000 cells/mL |
| Jul 12, 2025 | about 12,000 cells/mL |
| Jul 5, 2025 | about 12,000 cells/mL |
| Feb 22, 2025 | about 24,000 cells/mL |
| Feb 1, 2025 | about 120,000 cells/mL |
This is a satellite estimate from the U.S. EPA's Cyanobacteria Assessment Network, not an advisory. It estimates how much cyanobacteria is in the water near the lake's center, not whether toxins are present: a high number does not mean toxins, and a low one does not mean there are none. It covers lakes of about 1 square kilometer and larger, so small ponds, dog parks and most rivers are not covered, and clouds can hide a lake for weeks. It never changes the advisory status above.
Satellite estimates: U.S. EPA Cyanobacteria Assessment Network (CyAN), from Copernicus Sentinel-3 data. Provisional, research-level estimates; EPA does not endorse this site. Checked Oct 22, 2026.
Reported spots
The state records each report at a spot, such as a beach or a boat ramp. Each spot's latest deciding record:
| Spot | Status |
|---|---|
| Dam | Caution advisory, last posted Aug 11, 2026. No all-clear recorded. |
| West End (South Shore) | Caution advisory, last posted Sep 1, 2023. No all-clear recorded. |
| Indian Ole Rd west of town | Caution advisory, last posted Sep 1, 2023. No all-clear recorded. |
| Mountain Meadows Reservoir, near the dam | Caution advisory, last posted Sep 2, 2020. No all-clear recorded. |
| Mountain Meadows Reservoir | The state's latest record, from Sep 9, 2016, recommends no advisory. |
Advisory history
Every advisory record the state has published for Mountain Meadows Reservoir, newest first. "None" is the state's record that no advisory was recommended on that date. "NA" records do not change a status.
| Date | Spot | State's level | Notes |
|---|---|---|---|
| Aug 11, 2026 | Dam | Caution | Visual monitoring only-present bloom |
| Aug 11, 2026 | Dam | Caution | Visual monitoring only-present bloom |
| Sep 1, 2023 | West End (South Shore) | Caution | Advisory based on visual and toxins |
| Sep 1, 2023 | Indian Ole Rd west of town | Caution | Advisory based on visual and toxins; Under investigation |
| Sep 2, 2020 | Mountain Meadows Reservoir, near the dam | Caution | visual monitoring based advisory |
| Sep 9, 2016 | Mountain Meadows Reservoir | None |
Source
Advisory data: California State Water Resources Control Board, Freshwater Harmful Algal Bloom Program, via data.ca.gov (public domain). Advisories are recommendations; reporting is voluntary and incomplete. The state's data. An advisory ends only when the state records a later "None" (no advisory recommended) at the same spot, or an end date. A blank end date is unknown.