Lake San Antonio: toxic algae advisories
Lake San Antonio, Monterey County. See all Monterey County waters.
What the state's records say
Danger advisory, last posted Sep 4, 2026. No all-clear recorded.
7 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 San Antonio
The state has an advisory on file for Lake San Antonio (Danger advisory), last posted Sep 4, 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 May 30, 2026: about 56,000 cells/mL of cyanobacteria near the center of Lake San Antonio.
A satellite estimate from EPA CyAN for a 3.3 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| May 30, 2026 | about 56,000 cells/mL |
| May 9, 2026 | about 400,000 cells/mL |
| May 2, 2026 | about 1,100,000 cells/mL |
| Apr 25, 2026 | about 550,000 cells/mL |
| Oct 25, 2025 | about 8,800 cells/mL |
| Oct 18, 2025 | about 22,000 cells/mL |
| Oct 11, 2025 | about 19,000 cells/mL |
| Aug 2, 2025 | about 82,000 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 |
|---|---|
| Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness, last posted Sep 4, 2026. No all-clear recorded. |
| Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | General awareness, last posted Sep 4, 2026. No all-clear recorded. |
| open water | General awareness, last posted Aug 4, 2026. No all-clear recorded. |
| Lake San Antonio at Harris Creek Launch Dock (309SANTHD) | General awareness, last posted Aug 4, 2026. No all-clear recorded. |
| unspecified location | Reports on file, with no advisory level the state has classified. |
| Spot not described | The state's latest record, from May 27, 2021, recommends no advisory. |
| Lake San Antonio | Caution advisory, last posted Aug 31, 2020. No all-clear recorded. |
| Lake San Antonio | Caution advisory, last posted Aug 31, 2018. No all-clear recorded. |
| Lake San Antonio | Danger advisory, last posted Jun 29, 2017. No all-clear recorded. |
Advisory history
Every advisory record the state has published for Lake San Antonio, 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 4, 2026 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Alert-high concentration toxins; Posted general awareness; Updates from routine monitoring program-organization |
| Sep 4, 2026 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | General awareness | Posted general awareness; Updates from routine monitoring program-organization |
| Sep 4, 2026 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | None | Alert-high concentration toxins; Posted general awareness; Updates from routine monitoring program-organization |
| Sep 4, 2026 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | None | Posted general awareness; Updates from routine monitoring program-organization |
| Aug 4, 2026 | open water | General awareness | |
| Aug 4, 2026 | Lake San Antonio at Harris Creek Launch Dock (309SANTHD) | General awareness | Updates from routine monitoring program-organization |
| Jun 25, 2026 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Alert-high concentration toxins; Posted general awareness; Updates from routine monitoring program-organization |
| Jun 25, 2026 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Alert-high concentration toxins; Posted general awareness; Updates from routine monitoring program-organization |
| Jun 25, 2026 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | General awareness | Posted general awareness; Updates from routine monitoring program-organization |
| Jun 4, 2026 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Alert-high concentration toxins; Posted general awareness; Updates from routine monitoring program-organization |
| May 22, 2026 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Alert-high concentration toxins; Posted general awareness; Updates from routine monitoring program-organization |
| May 22, 2026 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | General awareness | Posted general awareness; Updates from routine monitoring program-organization |
| Aug 28, 2025 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | General awareness | Updates from routine monitoring program-organization |
| Aug 28, 2025 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Advisory based on visual and toxins; Alert-high concentration toxins; Updates from routine monitoring program-organization |
| Aug 28, 2025 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | None | Advisory based on visual and toxins; Alert-high concentration toxins; Updates from routine monitoring program-organization |
| Aug 28, 2025 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | None | Updates from routine monitoring program-organization |
| Aug 28, 2025 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | None | Advisory based on visual and toxins; Alert-high concentration toxins; Updates from routine monitoring program-organization |
| Aug 28, 2025 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | None | Updates from routine monitoring program-organization |
| Jun 30, 2025 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | General awareness | Updates from routine monitoring program-organization |
| Jun 30, 2025 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | None | Updates from routine monitoring program-organization |
| May 23, 2025 | unspecified location | Blank in the state's file | Suspected illness reported; Under investigation |
| May 15, 2025 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Advisory based on visual and toxins; Alert-high concentration toxins; Updates from routine monitoring program-organization |
| May 15, 2025 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | None | Advisory based on visual and toxins; Alert-high concentration toxins; Updates from routine monitoring program-organization |
| May 15, 2025 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Advisory based on visual and toxins; Alert-high concentration toxins; Updates from routine monitoring program-organization |
| May 15, 2025 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | None | Advisory based on visual and toxins; Alert-high concentration toxins; Updates from routine monitoring program-organization |
| Jun 28, 2024 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | None | Updates from routine monitoring program-organization |
| Jun 28, 2024 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | General awareness | Updates from routine monitoring program-organization |
| May 21, 2024 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Advisory based on visual and toxins; Alert-high concentration toxins; Updates from routine monitoring program-organization |
| May 21, 2024 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | Caution | Lake-wide advisory; Updates from routine monitoring program-organization |
| May 21, 2024 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Caution | Advisory based on visual and toxins; Alert-high concentration toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| May 21, 2024 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Advisory based on visual and toxins; Alert-high concentration toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| May 21, 2024 | Lake San Antonio at North Shore McCandless Springs Campground (309SANTMC) | General awareness | Updates from routine monitoring program-organization |
| Aug 31, 2023 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Caution | Advisory based on visual and toxins; Alert-high concentration toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| Aug 7, 2023 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Caution | Advisory based on visual and toxins; Alert-high concentration toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| Jun 29, 2023 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Danger | Advisory based on visual and toxins; Alert-high concentration toxins; Lake-wide advisory; Updates from routine monitoring program-organization |
| May 25, 2023 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Caution | Advisory based on visual and toxins; Lake-wide advisory |
| May 25, 2023 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Caution | Advisory based on visual and toxins |
| Apr 28, 2023 | Lake San Antonio at Harris Creek Launch Dock (309SANTHD) | Caution | Updates from routine monitoring program-organization |
| Apr 28, 2023 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Caution | visual monitoring based advisory |
| Dec 9, 2022 | Lake San Antonio at Harris Creek Launch Dock (309SANTHD) | General awareness | Updates from routine monitoring program-organization |
| Dec 9, 2022 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Advisory based on visual and toxins |
| Nov 28, 2022 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | General awareness | Advisory based on visual and toxins |
| Nov 28, 2022 | Lake San Antonio at Harris Creek Launch Dock (309SANTHD) | None | Updates from routine monitoring program-organization |
| Nov 10, 2022 | Lake San Antonio at Harris Creek Launch Dock (309SANTHD) | None | Updates from routine monitoring program-organization |
| Nov 10, 2022 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Caution | Advisory based on visual and toxins |
| Oct 19, 2022 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Danger | Advisory based on visual and toxins |
| Jul 1, 2022 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Danger | Advisory based on visual and toxins |
| Jun 30, 2022 | Lake San Antonio at Harris Creek Launch Dock (309SANTHD) | Caution | Updates from routine monitoring program-organization |
| Jun 30, 2022 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Caution | Advisory based on visual and toxins |
| May 27, 2022 | Lake San Antonio at Harris Creek Launch Dock (309SANTHD) | Caution | Updates from routine monitoring program-organization |
| May 27, 2022 | Lake San Antonio at Harris Creek Launch Dock (309SANTHD) | Caution | Updates from routine monitoring program-organization |
| May 27, 2022 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | Caution | Advisory based on visual and toxins |
| May 27, 2022 | Lake San Antonio at South Shore (309SANTBE) Marina Launch | None | Updates from routine monitoring program-organization |
| May 27, 2021 | Spot not described | None | Testing results below posting triggers |
| Aug 31, 2020 | Lake San Antonio | Caution | visual monitoring based advisory |
| Aug 31, 2018 | Lake San Antonio | Caution | |
| Jun 29, 2017 | Lake San Antonio | 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.