Donner Lake: toxic algae advisories
Donner Lake, Nevada County. See all Nevada County waters.
What the state's records say
The state's latest record, from Sep 30, 2022, recommends no advisory.
That reflects what the state knew on that date. It is not a finding that the water is safe now: blooms can return within days, and many are never reported.
Before you go, check the state's official algae page and any signs posted at the water.
Dogs at Donner Lake
The state's latest record, from Sep 30, 2022, recommends no advisory. For Donner Lake, that is not the same as an all-clear for today. Look at the water before your dog goes in: keep it out of green, blue-green or scummy water and away from mats on the shore.
Satellite estimate (not an advisory)
Week ending Oct 17, 2026: about 18,000 cells/mL of cyanobacteria near the center of Donner Lake.
A satellite estimate from EPA CyAN for a 3.4 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Oct 17, 2026 | about 18,000 cells/mL |
| Sep 26, 2026 | about 7,400 cells/mL |
| Feb 7, 2026 | about 31,000 cells/mL |
| Jan 24, 2026 | about 26,000 cells/mL |
| Dec 6, 2025 | about 16,000 cells/mL |
| Nov 29, 2025 | about 30,000 cells/mL |
| Aug 23, 2025 | about 21,000 cells/mL |
| Mar 29, 2025 | about 15,000 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 |
|---|---|
| Outfall | The state's latest record, from Sep 30, 2022, recommends no advisory. |
| Spot not described | The state's latest record, from Jun 11, 2021, recommends no advisory. |
Advisory history
Every advisory record the state has published for Donner Lake, 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 |
|---|---|---|---|
| Sep 30, 2022 | Outfall | None | No cyano, other algae present. |
| Aug 24, 2022 | Outfall | None | No cyano, other algae present. |
| Jul 5, 2022 | Outfall | None | No cyano, other algae present. |
| Jun 11, 2021 | Spot not described | None | Testing results below posting triggers |
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.