Lake Siskiyou: toxic algae advisories
Lake Siskiyou, Siskiyou County. See all Siskiyou County waters.
What the state's records say
The state's latest record, from Sep 8, 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 Lake Siskiyou
The state's latest record, from Sep 8, 2022, recommends no advisory. For Lake Siskiyou, 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 Jun 27, 2026: about 25,000 cells/mL of cyanobacteria near the center of Lake Siskiyou.
A satellite estimate from EPA CyAN for a 1.8 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Jun 27, 2026 | about 25,000 cells/mL |
| Feb 7, 2026 | about 74,000 cells/mL |
| Jan 24, 2026 | about 70,000 cells/mL |
| Jan 17, 2026 | about 270,000 cells/mL |
| Dec 6, 2025 | about 120,000 cells/mL |
| Nov 15, 2025 | about 38,000 cells/mL |
| Aug 16, 2025 | about 12,000 cells/mL |
| Jan 25, 2025 | about 76,000 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 North Side | The state's latest record, from Sep 8, 2022, recommends no advisory. |
| Cable Beach | The state's latest record, from Sep 8, 2022, recommends no advisory. |
| Meadows | The state's latest record, from Sep 8, 2022, recommends no advisory. |
| Boat Launch | The state's latest record, from Sep 8, 2022, recommends no advisory. |
Advisory history
Every advisory record the state has published for Lake Siskiyou, 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 8, 2022 | Dam North Side | None | No cyano bloom w/testing |
| Sep 8, 2022 | Cable Beach | None | No cyano bloom w/testing |
| Sep 8, 2022 | Meadows | None | No cyano bloom w/testing |
| Sep 8, 2022 | Boat Launch | None | No cyano bloom w/testing |
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.