Lake Arrowhead: toxic algae advisories
Lake Arrowhead, San Bernardino County. See all San Bernardino County waters.
What the state's records say
The state's latest record, from Sep 2, 2022, recommends no advisory.
Last advisory on file: Aug 19, 2022.
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 Arrowhead
The state's latest record, from Sep 2, 2022, recommends no advisory. For Lake Arrowhead, 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 Aug 8, 2026: about 11,000 cells/mL of cyanobacteria near the center of Lake Arrowhead.
A satellite estimate from EPA CyAN for a 3.0 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Aug 8, 2026 | about 11,000 cells/mL |
| Dec 13, 2025 | about 17,000 cells/mL |
| Dec 6, 2025 | about 14,000 cells/mL |
| Nov 15, 2025 | about 20,000 cells/mL |
| Nov 8, 2025 | about 19,000 cells/mL |
| Nov 1, 2025 | about 22,000 cells/mL |
| Oct 25, 2025 | about 7,000 cells/mL |
| Oct 11, 2025 | about 23,000 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 |
|---|---|
| Burnt Mill Beach Club | The state's latest record, from Sep 2, 2022, recommends no advisory. |
| Tavern Bay | The state's latest record, from Sep 2, 2022, recommends no advisory. |
Advisory history
Every advisory record the state has published for Lake Arrowhead, 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 2, 2022 | Burnt Mill Beach Club | None | End date recorded: Dec 27, 2022. No cyano bloom w/testing |
| Sep 2, 2022 | Burnt Mill Beach Club | None | No cyano bloom w/testing |
| Sep 2, 2022 | Tavern Bay | None | No cyano bloom w/testing |
| Sep 2, 2022 | Burnt Mill Beach Club | None | No cyano, other algae present. |
| Sep 2, 2022 | Tavern Bay | None | No cyano bloom w/testing |
| Aug 19, 2022 | Tavern Bay | Caution | Lake-wide advisory; Suspected illness reported; Under investigation |
| Jun 30, 2022 | Burnt Mill Beach Club | None | No cyano, other algae present. |
| Jun 30, 2022 | Tavern Bay | 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.