Stone Lagoon: toxic algae advisories
Stone Lagoon, Humboldt County. See all Humboldt County waters.
What the state's records say
Danger advisory, last posted Oct 19, 2020. No all-clear recorded.
2 reported spots here have an advisory with no all-clear recorded.
Reporting is voluntary, so the state may not have recorded an end even if conditions changed. Check posted signs and the official map.
What this level asks: Toxins may be at levels that can seriously harm people and animals. Stay out of the water and keep children and pets away from the water and the shore.
Before you go, check the state's official algae page and any signs posted at the water.
Dogs at Stone Lagoon
The state has an advisory on file for Stone Lagoon (Danger advisory), last posted Oct 19, 2020, and no all-clear recorded. Keep your dog out of the water and away from scum on the shore until the state records an end.
Satellite estimate (not an advisory)
Week ending Jul 4, 2026: about 66,000 cells/mL of cyanobacteria near the center of Stone Lagoon.
A satellite estimate from EPA CyAN for a 2.5 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Jul 4, 2026 | about 66,000 cells/mL |
| Jan 18, 2025 | about 130,000 cells/mL |
| Nov 30, 2024 | about 290,000 cells/mL |
| Jan 28, 2023 | about 170,000 cells/mL |
| Jan 21, 2023 | about 480,000 cells/mL |
| Oct 1, 2022 | about 47,000 cells/mL |
| Sep 24, 2022 | about 150,000 cells/mL |
| Sep 17, 2022 | about 260,000 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 |
|---|---|
| Boat Ramp | The state's latest record, from Jul 2, 2026, recommends no advisory. |
| Lagoonwide | The state's latest record, from Jun 26, 2023, recommends no advisory. |
| Spot not described | The state's latest record, from Jun 29, 2021, recommends no advisory. |
| North | The state's latest record, from Jun 22, 2021, recommends no advisory. |
| Boat Ramp | The state's latest record, from Jun 22, 2021, recommends no advisory. |
| Stone Lagoon | Warning advisory, last posted Oct 19, 2020. No all-clear recorded. |
| Stone Lagoon - South of Campground Beach | Danger advisory, last posted Aug 31, 2018. No all-clear recorded. |
Advisory history
Every advisory record the state has published for Stone Lagoon, 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 |
|---|---|---|---|
| Jul 2, 2026 | Boat Ramp | None | Testing results below posting triggers |
| May 21, 2026 | Boat Ramp | Caution | Advisory based on visual and toxins |
| May 21, 2026 | Boat Ramp | None | Advisory based on visual and toxins |
| May 21, 2026 | Boat Ramp | None | Advisory based on visual and toxins |
| Oct 22, 2025 | Boat Ramp | None | No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| Aug 28, 2025 | Boat Ramp | None | No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| Jun 18, 2025 | Boat Ramp | None | No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| May 20, 2025 | Boat Ramp | None | No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| Oct 23, 2024 | Boat Ramp | None | No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| Aug 27, 2024 | Boat Ramp | None | No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| Jun 26, 2024 | Boat Ramp | None | No cyano bloom w/testing; Testing results below posting triggers; Updates from routine monitoring program-organization |
| May 21, 2024 | Boat Ramp | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Oct 19, 2023 | Boat Ramp | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Oct 19, 2023 | Boat Ramp | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Aug 24, 2023 | Boat Ramp | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Jun 26, 2023 | Lagoonwide | None | End date recorded: Oct 24, 2022. Testing results below posting triggers; Updates from routine monitoring program-organization |
| Oct 24, 2022 | Lagoonwide | None | End date recorded: Oct 24, 2022. Testing results below posting triggers; Updates from routine monitoring program-organization |
| Oct 24, 2022 | Lagoonwide | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Sep 1, 2022 | Lagoonwide | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Sep 1, 2022 | Lagoonwide | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Jun 28, 2022 | Lagoonwide | None | Updates from routine monitoring program-organization |
| May 31, 2022 | Lagoonwide | None | Updates from routine monitoring program-organization |
| Jun 29, 2021 | Spot not described | None | Testing results below posting triggers |
| Jun 22, 2021 | North | None | Testing results below posting triggers |
| Jun 22, 2021 | Boat Ramp | None | Testing results below posting triggers |
| Oct 19, 2020 | Stone Lagoon | Warning | Advisory based on visual and toxins |
| Aug 31, 2018 | Stone Lagoon - South of Campground Beach | Danger |
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.