San Diego River: toxic algae advisories
San Diego River, San Diego County. See all San Diego County waters.
What the state's records say
Warning advisory, last posted Aug 25, 2023. 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 harm people and animals. Do not swim or let children or pets in the water, and stay away from scum.
Before you go, check the state's official algae page and any signs posted at the water.
Dogs at San Diego River
The state has an advisory on file for San Diego River (Warning advisory), last posted Aug 25, 2023, 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.
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 |
|---|---|
| Old Man's Pond between Magnolia Ave and Cuyamaca St | The state's latest record, from Sep 14, 2026, recommends no advisory. |
| San Diego River, Sefton Park | The state's latest record, from Aug 31, 2026, recommends no advisory. |
| Upstream of San Diego Mission Road | The state's latest record, from Nov 13, 2025, recommends no advisory. |
| Old Mission Dam | The state's latest record, from Oct 21, 2025, recommends no advisory. |
| Upstream end of Walker Preserve | The state's latest record, from Aug 25, 2025, recommends no advisory. |
| Mission Basilica San Diego De Alcala | The state's latest record, from Oct 21, 2024, recommends no advisory. |
| Cuyamaca Street | The state's latest record, from Oct 3, 2024, recommends no advisory. |
| at YMCA | Algal mat alert sign, last posted Aug 25, 2023. No all-clear recorded. |
| San Diego River at RCP ponds in Walker Preserve | The state's latest record, from Aug 29, 2022, recommends no advisory. |
| San Diego River at YMCA | The state's latest record, from Aug 24, 2022, recommends no advisory. |
| east of Mast Park | The state's latest record, from Nov 5, 2021, recommends no advisory. |
| Kaiser Ponds | The state's latest record, from Sep 14, 2021, recommends no advisory. |
| at Old Mission Dam | The state's latest record, from Jul 1, 2021, recommends no advisory. |
| San Diego River mainstem, just W. of I-805 | Warning advisory, last posted Aug 3, 2018. No all-clear recorded. |
Advisory history
Every advisory record the state has published for San Diego River, 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 14, 2026 | Old Man's Pond between Magnolia Ave and Cuyamaca St | None | Confirmed no bloom |
| Aug 31, 2026 | San Diego River, Sefton Park | None | Confirmed no bloom |
| Aug 31, 2026 | Old Man's Pond between Magnolia Ave and Cuyamaca St | Caution | Advisory based on visual and toxins |
| Jul 1, 2026 | San Diego River, Sefton Park | None | |
| Jul 1, 2026 | Old Man's Pond between Magnolia Ave and Cuyamaca St | None | No cyano bloom w/testing |
| May 11, 2026 | Old Man's Pond between Magnolia Ave and Cuyamaca St | None | No cyano bloom w/testing |
| May 11, 2026 | Old Man's Pond between Magnolia Ave and Cuyamaca St | None | No cyano bloom w/testing |
| May 7, 2026 | Old Man's Pond between Magnolia Ave and Cuyamaca St | None | |
| Nov 13, 2025 | Upstream of San Diego Mission Road | None | No cyano bloom w/testing |
| Nov 6, 2025 | Upstream of San Diego Mission Road | None | Under investigation |
| Oct 21, 2025 | Old Mission Dam | None | No cyano bloom w/testing |
| Aug 25, 2025 | Old Mission Dam | Caution | Advisory based on visual and toxins |
| Aug 25, 2025 | Upstream end of Walker Preserve | None | No cyano bloom w/testing |
| Jul 1, 2025 | Old Mission Dam | None | No cyano bloom w/testing |
| Jul 1, 2025 | Upstream end of Walker Preserve | None | No cyano bloom w/testing |
| May 14, 2025 | Old Mission Dam | None | No cyano bloom w/testing |
| May 14, 2025 | Upstream end of Walker Preserve | None | No cyano bloom w/testing |
| May 14, 2025 | Upstream end of Walker Preserve | Blank in the state's file | No cyano bloom w/testing |
| May 14, 2025 | Old Mission Dam | Blank in the state's file | No cyano bloom w/testing |
| Oct 21, 2024 | Mission Basilica San Diego De Alcala | None | Testing results below posting triggers |
| Oct 4, 2024 | Mission Basilica San Diego De Alcala | Caution | Visual monitoring only-present bloom |
| Oct 3, 2024 | Cuyamaca Street | None | End date recorded: Oct 3, 2024. Visual monitoring only-absent bloom |
| Sep 12, 2024 | Mission Basilica San Diego De Alcala | Caution | Visual monitoring only-present bloom |
| Aug 25, 2023 | at YMCA | Algal mat alert sign | No cyano bloom w/testing; Updates from routine monitoring program-organization |
| Jun 28, 2023 | at YMCA | None | No cyano bloom w/testing; Updates from routine monitoring program-organization |
| May 23, 2023 | at YMCA | None | No cyano bloom w/testing; Updates from routine monitoring program-organization |
| Aug 29, 2022 | San Diego River at RCP ponds in Walker Preserve | None | No cyano bloom w/testing |
| Aug 25, 2022 | San Diego River at RCP ponds in Walker Preserve | None | End date recorded: Aug 25, 2022. No cyano bloom w/testing |
| Aug 25, 2022 | San Diego River at RCP ponds in Walker Preserve | None | No cyano bloom w/testing |
| Aug 24, 2022 | San Diego River at YMCA | None | Testing results below posting triggers |
| Aug 16, 2022 | San Diego River at YMCA | Caution | Suspected bloom, investigation ongoing |
| Jun 29, 2022 | San Diego River at RCP ponds in Walker Preserve | None | Testing results below posting triggers |
| May 16, 2022 | San Diego River at RCP ponds in Walker Preserve | None | No cyano, other algae present. |
| May 16, 2022 | San Diego River at RCP ponds in Walker Preserve | None | No cyano, other algae present. |
| Nov 5, 2021 | east of Mast Park | None | Testing results below posting triggers |
| Sep 14, 2021 | Kaiser Ponds | None | Testing results below posting triggers |
| Jul 1, 2021 | at Old Mission Dam | None | Testing results below posting triggers |
| Aug 3, 2018 | San Diego River mainstem, just W. of I-805 | Warning |
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.