Ruth Lake: toxic algae advisories
Ruth Lake, Trinity County. See all Trinity County waters.
What the state's records say
Caution advisory, last posted May 27, 2021. No all-clear recorded.
3 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: Algae that can make toxins may be present. Keep people, children and pets away from algae and scum, and do not let pets drink the water.
Before you go, check the state's official algae page and any signs posted at the water.
Dogs at Ruth Lake
The state has an advisory on file for Ruth Lake (Caution advisory), last posted May 27, 2021, 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 Dec 27, 2025: about 45,000 cells/mL of cyanobacteria near the center of Ruth Lake.
A satellite estimate from EPA CyAN for a 4.3 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Dec 27, 2025 | about 45,000 cells/mL |
| Dec 13, 2025 | about 860,000 cells/mL |
| Nov 29, 2025 | about 840,000 cells/mL |
| Dec 30, 2023 | about 63,000 cells/mL |
| Nov 26, 2022 | about 24,000 cells/mL |
| Nov 28, 2020 | about 19,000 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 |
|---|---|
| Campground (109RLCMPG) | The state's latest record, from Sep 2, 2026, recommends no advisory. |
| Lakewide | The state's latest record, from Nov 14, 2022, recommends no advisory. |
| South Lake | The state's latest record, from Jul 6, 2021, recommends no advisory. |
| East Beach | The state's latest record, from Jul 6, 2021, recommends no advisory. |
| at Dillon Cove | The state's latest record, from Jul 6, 2021, recommends no advisory. |
| South | Algal mat general awareness sign, last posted May 27, 2021. No all-clear recorded. |
| North | Algal mat general awareness sign, last posted May 27, 2021. No all-clear recorded. |
| eastern side along hwy 504 | Caution advisory, last posted Apr 26, 2021. No all-clear recorded. |
Advisory history
Every advisory record the state has published for Ruth 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 |
|---|---|---|---|
| Sep 2, 2026 | Campground (109RLCMPG) | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Jun 25, 2026 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Jun 25, 2026 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| May 14, 2026 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Nov 6, 2025 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Aug 20, 2025 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Jun 18, 2025 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Oct 25, 2024 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Aug 22, 2024 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Jul 1, 2024 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Oct 30, 2023 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Aug 28, 2023 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Jul 5, 2023 | Campground (109RLCMPG) | None | No cyano bloom w/testing; Testing results below posting triggers |
| Nov 14, 2022 | Lakewide | None | End date recorded: Nov 14, 2022. De-posting advisory. |
| Nov 14, 2022 | Lakewide | None | De-posting advisory. |
| Oct 28, 2022 | Lakewide | Caution | Advisory based on visual and toxins; Suspected illness reported; Updates from routine monitoring program-organization |
| Oct 18, 2022 | Lakewide | Caution | Advisory based on visual and toxins; Suspected illness reported; Updates from routine monitoring program-organization |
| Sep 14, 2022 | Lakewide | Caution | Advisory based on visual and toxins; Suspected illness reported; Updates from routine monitoring program-organization |
| Sep 9, 2022 | Lakewide | Caution | Advisory based on visual and toxins; Bottom/benthic bloom observed; Suspected illness reported |
| Sep 7, 2022 | Lakewide | Caution | Lake-wide advisory; Suspected bloom, investigation ongoing; Suspected illness reported |
| Jun 21, 2022 | Lakewide | None | Updates from routine monitoring program-organization |
| May 31, 2022 | Lakewide | None | Updates from routine monitoring program-organization |
| May 31, 2022 | Lakewide | None | Updates from routine monitoring program-organization |
| Jul 6, 2021 | South Lake | None | Testing results below posting triggers |
| Jul 6, 2021 | East Beach | None | Testing results below posting triggers |
| Jul 6, 2021 | at Dillon Cove | None | Testing results below posting triggers |
| May 27, 2021 | South | Algal mat general awareness sign | |
| May 27, 2021 | North | Algal mat general awareness sign | |
| Apr 26, 2021 | eastern side along hwy 504 | Caution | visual monitoring based advisory |
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.