Grant Lake: toxic algae advisories
Grant Lake, Mono County. See all Mono County waters.
What the state's records say
The state's latest record, from Oct 7, 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 Grant Lake
The state's latest record, from Oct 7, 2026, recommends no advisory. For Grant 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 11,000 cells/mL of cyanobacteria near the center of Grant Lake.
A satellite estimate from EPA CyAN for a 4.5 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Oct 17, 2026 | about 11,000 cells/mL |
| Oct 10, 2026 | about 13,000 cells/mL |
| Sep 12, 2026 | about 6,900 cells/mL |
| Aug 22, 2026 | about 9,600 cells/mL |
| Jul 18, 2026 | about 7,700 cells/mL |
| May 16, 2026 | about 10,000 cells/mL |
| May 2, 2026 | about 15,000 cells/mL |
| Apr 11, 2026 | about 22,000 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 |
|---|---|
| Marina | The state's latest record, from Oct 7, 2026, recommends no advisory. |
| Outlet | The state's latest record, from Oct 14, 2022, recommends no advisory. |
| Marina | The state's latest record, from Aug 29, 2022, recommends no advisory. |
| Grant Lake marina | The state's latest record, from May 26, 2022, recommends no advisory. |
Advisory history
Every advisory record the state has published for Grant 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 |
|---|---|---|---|
| Oct 7, 2026 | Marina | None | Advisory based on visual and toxins |
| Sep 2, 2026 | Marina | None | Advisory based on visual and toxins |
| Jun 18, 2026 | Marina | None | Advisory based on visual and toxins |
| Oct 23, 2025 | Marina | None | Advisory based on visual and toxins |
| Aug 29, 2025 | Marina | None | Advisory based on visual and toxins |
| Jun 25, 2025 | Marina | None | Advisory based on visual and toxins |
| Oct 4, 2024 | Marina | None | Advisory based on visual and toxins; No cyano bloom w/testing; Updates from routine monitoring program-organization |
| Aug 22, 2024 | Marina | None | Advisory based on visual and toxins; No cyano bloom w/testing; Updates from routine monitoring program-organization |
| Jun 27, 2024 | Marina | None | No cyano bloom w/testing; Updates from routine monitoring program-organization |
| Aug 22, 2023 | Marina | None | No cyano bloom w/testing; Updates from routine monitoring program-organization |
| Jun 27, 2023 | Marina | None | No cyano bloom w/testing; Updates from routine monitoring program-organization |
| Oct 14, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Oct 14, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Aug 29, 2022 | Marina | None | Updates from routine monitoring program-organization |
| Aug 17, 2022 | Marina | None | visual monitoring based advisory |
| Jun 29, 2022 | Marina | None | Updates from routine monitoring program-organization |
| May 26, 2022 | Grant Lake marina | None | Updates from routine monitoring program-organization |
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.