Lake Hemet: toxic algae advisories
Lake Hemet, Riverside County. See all Riverside County waters.
What the state's records say
Danger advisory, last posted Sep 2, 2026. No all-clear recorded.
8 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 Lake Hemet
The state has an advisory on file for Lake Hemet (Danger advisory), last posted Sep 2, 2026, 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 Oct 17, 2026: about 910,000 cells/mL of cyanobacteria near the center of Lake Hemet.
A satellite estimate from EPA CyAN for a 1.4 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Oct 17, 2026 | about 910,000 cells/mL |
| Oct 10, 2026 | about 840,000 cells/mL |
| Oct 3, 2026 | about 670,000 cells/mL |
| Sep 26, 2026 | about 510,000 cells/mL |
| Sep 19, 2026 | about 860,000 cells/mL |
| Sep 12, 2026 | about 1,300,000 cells/mL |
| Sep 5, 2026 | about 510,000 cells/mL |
| Aug 29, 2026 | about 940,000 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 |
|---|---|
| northwest shore (802LHN004) | Danger advisory, last posted Sep 2, 2026. No all-clear recorded. |
| boat launch-campground (802LHBL1) | Caution advisory, last posted Sep 2, 2026. No all-clear recorded. |
| marina and open water on east side | Caution advisory, last posted Oct 18, 2024. No all-clear recorded. |
| North east shore | The state's latest record, from May 24, 2023, recommends no advisory. |
| northwest shore | Danger advisory, last posted Nov 23, 2022. No all-clear recorded. |
| North east shore | Caution advisory, last posted Aug 27, 2022. No all-clear recorded. |
| Idyllwild, CA | Caution advisory, last posted Aug 18, 2022. No all-clear recorded. |
| Lake Hemet-North Shore | The state's latest record, from Nov 20, 2020, recommends no advisory. |
| Lake Hemet Campground- Boat Launch Ramp | The state's latest record, from Nov 20, 2020, recommends no advisory. |
| Lake Hemet Campground-North East Corner | Danger advisory, last posted Sep 11, 2020. No all-clear recorded. |
| Lake Hemet, north west shore | Caution advisory, last posted Jul 8, 2020. No all-clear recorded. |
Advisory history
Every advisory record the state has published for Lake Hemet, 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 | northwest shore (802LHN004) | Danger | Advisory based on visual and toxins; Alert-high concentration toxins; Floating/planktonic bloom observed |
| Sep 2, 2026 | boat launch-campground (802LHBL1) | Caution | Advisory based on visual and toxins |
| Sep 2, 2026 | boat launch-campground (802LHBL1) | Caution | Advisory based on visual and toxins |
| Sep 2, 2026 | northwest shore (802LHN004) | Danger | Advisory based on visual and toxins; Alert-high concentration toxins; Floating/planktonic bloom observed |
| Sep 2, 2026 | boat launch-campground (802LHBL1) | Caution | Advisory based on visual and toxins |
| Sep 2, 2026 | boat launch-campground (802LHBL1) | Danger | Advisory based on visual and toxins; Alert-high concentration toxins |
| Jul 1, 2026 | boat launch-campground (802LHBL1) | Caution | Advisory based on visual and toxins; Floating/planktonic bloom observed; Lake-wide advisory |
| Jul 1, 2026 | boat launch-campground (802LHBL1) | General awareness | Advisory based on visual and toxins; Floating/planktonic bloom observed; Lake-wide advisory |
| Jul 1, 2026 | northwest shore (802LHN004) | Caution | Advisory based on visual and toxins; Floating/planktonic bloom observed; Lake-wide advisory |
| May 14, 2026 | boat launch-campground (802LHBL1) | General awareness | Advisory based on visual and toxins; Updates from routine monitoring program-organization |
| May 14, 2026 | northwest shore (802LHN004) | Caution | Floating/planktonic bloom observed; Testing results below posting triggers; Updates from routine monitoring program-organization |
| Oct 17, 2025 | northwest shore (802LHN004) | Danger | Alert-high concentration toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| Oct 10, 2025 | northwest shore (802LHN004) | Caution | Alert-high concentration toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| Aug 19, 2025 | northwest shore (802LHN004) | Danger | Alert-high concentration toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| Jun 27, 2025 | northwest shore (802LHN004) | Caution | Lake-wide advisory; Updates from routine monitoring program-organization |
| May 21, 2025 | northwest shore (802LHN004) | None | Lake-wide advisory; Updates from routine monitoring program-organization |
| Nov 27, 2024 | boat launch-campground (802LHBL1) | Caution | Advisory based on visual and toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| Oct 18, 2024 | marina and open water on east side | Caution | Lake-wide advisory; Visual monitoring only-present bloom |
| Aug 26, 2024 | northwest shore (802LHN004) | Caution | Lake-wide advisory; Updates from routine monitoring program-organization |
| Aug 26, 2024 | boat launch-campground (802LHBL1) | Caution | Advisory based on visual and toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| Jun 17, 2024 | boat launch-campground (802LHBL1) | Caution | Advisory based on visual and toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| May 17, 2024 | northwest shore (802LHN004) | Danger | Advisory based on visual and toxins; Updates from routine monitoring program-organization |
| Aug 25, 2023 | boat launch-campground (802LHBL1) | Caution | Advisory based on visual and toxins; Lake-wide advisory; Updates from routine monitoring program-organization; visual monitoring based advisory |
| Jun 22, 2023 | boat launch-campground (802LHBL1) | Caution | Advisory based on visual and toxins; Lake-wide advisory; Updates from routine monitoring program-organization; visual monitoring based advisory |
| Jun 22, 2023 | boat launch-campground (802LHBL1) | Visual observation | Testing results below posting triggers; Updates from routine monitoring program-organization; visual monitoring based advisory |
| May 24, 2023 | North east shore | None | Updates from routine monitoring program-organization |
| May 24, 2023 | North east shore | None | Updates from routine monitoring program-organization |
| Nov 23, 2022 | northwest shore | Danger | Advisory based on visual and toxins; Alert-high concentration toxins |
| Oct 27, 2022 | northwest shore | Danger | Advisory based on visual and toxins; Alert-high concentration toxins |
| Aug 27, 2022 | North east shore | Caution | Advisory based on visual and toxins |
| Aug 18, 2022 | Idyllwild, CA | Caution | Under investigation |
| Aug 12, 2022 | Idyllwild, CA | NA - refer to Report Details | Under investigation |
| Jun 27, 2022 | North east shore | Caution | Advisory based on visual and toxins |
| Jun 22, 2022 | North east shore | None | Advisory based on visual and toxins |
| May 27, 2022 | North east shore | Caution | Advisory based on visual and toxins |
| Nov 20, 2020 | Lake Hemet-North Shore | None | Rec general awareness |
| Nov 20, 2020 | Lake Hemet Campground- Boat Launch Ramp | None | Rec general awareness |
| Sep 11, 2020 | Lake Hemet Campground-North East Corner | Danger | Advisory based on visual and toxins |
| Jul 8, 2020 | Lake Hemet, north west shore | 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.