Lake Sonoma: toxic algae advisories
Lake Sonoma, Sonoma County. See all Sonoma County waters.
What the state's records say
The state's latest record, from Aug 27, 2026, 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 Lake Sonoma
The state's latest record, from Aug 27, 2026, recommends no advisory. For Lake Sonoma, 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 Jan 17, 2026: about 52,000 cells/mL of cyanobacteria near the center of Lake Sonoma.
A satellite estimate from EPA CyAN for a 8.6 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Jan 17, 2026 | about 52,000 cells/mL |
| Jan 10, 2026 | about 100,000 cells/mL |
| Dec 27, 2025 | about 140,000 cells/mL |
| Nov 15, 2025 | about 340,000 cells/mL |
| Dec 23, 2023 | about 180,000 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 |
|---|---|
| Yorty Creek Recreation Area | The state's latest record, from Aug 27, 2026, recommends no advisory. |
| Public Boat Launch | The state's latest record, from Oct 12, 2022, recommends no advisory. |
Advisory history
Every advisory record the state has published for Lake Sonoma, 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 27, 2026 | Yorty Creek Recreation Area | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Aug 27, 2026 | Yorty Creek Recreation Area | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Jul 2, 2026 | Yorty Creek Recreation Area | None | End date recorded: Jun 30, 2022. Updates from routine monitoring program-organization |
| Oct 12, 2022 | Public Boat Launch | None | End date recorded: Oct 12, 2022. No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| Oct 12, 2022 | Public Boat Launch | None | No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| Sep 14, 2022 | Public Boat Launch | None | No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| Sep 14, 2022 | Public Boat Launch | None | No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| Jun 30, 2022 | Yorty Creek Recreation Area | None | End date recorded: Jun 30, 2022. No cyano, other algae present. |
| Jun 30, 2022 | Yorty Creek Recreation Area | None | No cyano, other algae present. |
| May 25, 2022 | Yorty Creek Recreation Area | None | No cyano, other algae present. |
| May 25, 2022 | Yorty Creek Recreation Area | None | No cyano, other algae present. |
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.