Diamond valley lake: toxic algae advisories
Diamond valley lake, Riverside County. See all Riverside County waters.
What the state's records say
Danger advisory, last posted May 8, 2026. 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 Diamond valley lake
The state has an advisory on file for Diamond valley lake (Danger advisory), last posted May 8, 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 7,000 cells/mL of cyanobacteria near the center of Diamond Valley Lake.
A satellite estimate from EPA CyAN for a 16.5 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Oct 17, 2026 | about 7,000 cells/mL |
| Jun 20, 2026 | about 80,000 cells/mL |
| Jun 6, 2026 | about 360,000 cells/mL |
| May 30, 2026 | about 650,000 cells/mL |
| May 23, 2026 | about 960,000 cells/mL |
| May 16, 2026 | about 1,200,000 cells/mL |
| May 9, 2026 | about 910,000 cells/mL |
| May 2, 2026 | about 640,000 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 |
|---|---|
| Hemet Ca | Caution advisory, last posted May 8, 2026. No all-clear recorded. |
| west of marina | The state's latest record, from Aug 21, 2025, recommends no advisory. |
| Diamond Valley Lake | Reports on file, with no advisory level the state has classified. |
| Diamond Valley Lake | Danger advisory, last posted Aug 31, 2018. No all-clear recorded. |
Advisory history
Every advisory record the state has published for Diamond valley 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 |
|---|---|---|---|
| May 8, 2026 | Hemet Ca | Caution | Updates from routine monitoring program-organization |
| May 5, 2026 | Hemet Ca | Caution | Updates from routine monitoring program-organization |
| Mar 30, 2026 | Hemet Ca | Caution | Updates from routine monitoring program-organization |
| Mar 19, 2026 | Hemet Ca | Caution | Updates from routine monitoring program-organization |
| Feb 18, 2026 | Hemet Ca | Caution | Updates from routine monitoring program-organization |
| Dec 22, 2025 | Hemet Ca | Caution | Updates from routine monitoring program-organization |
| Dec 19, 2025 | Hemet Ca | Blank in the state's file | Suspected bloom, investigation ongoing |
| Aug 21, 2025 | west of marina | None | Lake-wide advisory |
| Aug 20, 2025 | west of marina | Caution | Lake-wide advisory |
| Aug 15, 2025 | west of marina | Caution | Lake-wide advisory |
| Aug 7, 2025 | west of marina | Caution | Lake-wide advisory |
| Jul 17, 2025 | west of marina | None | End date recorded: Jul 17, 2025. Lake-wide advisory |
| Jul 11, 2025 | west of marina | Caution | Lake-wide advisory |
| Jul 2, 2025 | west of marina | Caution | Lake-wide advisory |
| Jun 10, 2025 | west of marina | Caution | Lake-wide advisory |
| Jun 10, 2025 | west of marina | Caution | Lake-wide advisory |
| Jun 10, 2025 | west of marina | None | Lake-wide advisory |
| Jan 27, 2025 | west of marina | None | Lake-wide advisory |
| Jan 13, 2025 | west of marina | General awareness | Lake-wide advisory |
| Dec 30, 2024 | west of marina | General awareness | Lake-wide advisory |
| Dec 17, 2024 | west of marina | General awareness | Lake-wide advisory |
| Dec 9, 2024 | west of marina | General awareness | Lake-wide advisory |
| Dec 2, 2024 | west of marina | General awareness | Lake-wide advisory |
| Jul 15, 2024 | west of marina | Caution | Lake-wide advisory |
| Jun 24, 2024 | west of marina | Caution | Lake-wide advisory |
| Jun 17, 2024 | west of marina | Caution | Lake-wide advisory |
| Jun 12, 2024 | west of marina | Caution | Lake-wide advisory |
| Jun 4, 2024 | west of marina | Caution | Lake-wide advisory |
| Jan 9, 2024 | west of marina | None | Lake-wide advisory |
| Jan 2, 2024 | west of marina | Caution | Lake-wide advisory |
| Dec 21, 2023 | west of marina | Caution | Lake-wide advisory |
| Dec 15, 2023 | west of marina | Caution | Lake-wide advisory |
| Dec 11, 2023 | west of marina | Caution | Lake-wide advisory |
| Dec 4, 2023 | west of marina | Caution | Lake-wide advisory |
| Nov 20, 2023 | west of marina | Caution | Lake-wide advisory |
| Nov 6, 2023 | west of marina | Caution | Lake-wide advisory |
| Oct 30, 2023 | west of marina | Caution | Lake-wide advisory |
| Oct 23, 2023 | west of marina | Caution | Lake-wide advisory |
| Oct 16, 2023 | west of marina | Caution | Lake-wide advisory |
| Oct 2, 2023 | west of marina | Caution | Lake-wide advisory |
| Sep 25, 2023 | west of marina | Caution | Lake-wide advisory |
| Sep 8, 2023 | west of marina | Caution | Lake-wide advisory |
| Aug 25, 2023 | west of marina | Caution | Lake-wide advisory |
| Jul 31, 2023 | west of marina | Caution | Lake-wide advisory |
| Jul 31, 2023 | west of marina | Caution | Lake-wide advisory |
| Jul 17, 2023 | west of marina | Caution | Lake-wide advisory |
| Jul 13, 2023 | west of marina | Caution | Lake-wide advisory |
| Jul 10, 2023 | west of marina | Warning | Lake-wide advisory |
| Jul 6, 2023 | west of marina | Warning | Lake-wide advisory |
| Jul 6, 2023 | west of marina | Warning | Lake-wide advisory |
| Aug 27, 2020 | Diamond Valley Lake | NA - refer to Report Details | |
| Aug 31, 2018 | Diamond Valley Lake | 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.