Lake Nacimiento: toxic algae advisories
Lake Nacimiento, San Luis Obispo County. See all San Luis Obispo County waters.
What the state's records say
General awareness, last posted Sep 4, 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: The state recorded an advisory of a type outside the Caution, Warning and Danger levels. Read the sign posted at the water.
Before you go, check the state's official algae page and any signs posted at the water.
Dogs at Lake Nacimiento
The state has an advisory on file for Lake Nacimiento (General awareness), 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)
No satellite reading on file for Lake Nacimiento in recent weeks. Clouds, ice, or a lake shape the satellite's estimate near its center misses can cause this. It is a gap in the data, not a reading.
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 Nacimiento at day use area | General awareness, last posted Sep 4, 2026. No all-clear recorded. |
| Lake Nacimiento at main marina launch | General awareness, last posted Sep 4, 2026. No all-clear recorded. |
| Lake Nacimiento at main marina launch | The state's latest record, from May 21, 2024, recommends no advisory. |
| Spot not described | The state's latest record, from May 27, 2021, recommends no advisory. |
| Lake Nacimiento | Reports on file, with no advisory level the state has classified. |
Advisory history
Every advisory record the state has published for Lake Nacimiento, 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 Nacimiento at day use area | General awareness | Updates from routine monitoring program-organization |
| Sep 4, 2026 | Lake Nacimiento at main marina launch | General awareness | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Sep 4, 2026 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| Sep 4, 2026 | Lake Nacimiento at main marina launch | None | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Jun 25, 2026 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| Jun 25, 2026 | Lake Nacimiento at main marina launch | None | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Aug 28, 2025 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| Aug 28, 2025 | Lake Nacimiento at main marina launch | None | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Jun 30, 2025 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| Jun 30, 2025 | Lake Nacimiento at main marina launch | None | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Jun 30, 2025 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| Jun 30, 2025 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| May 15, 2025 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| May 15, 2025 | Lake Nacimiento at main marina launch | None | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Aug 26, 2024 | Lake Nacimiento at day use area | General awareness | Updates from routine monitoring program-organization |
| Aug 26, 2024 | Lake Nacimiento at main marina launch | General awareness | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Jun 28, 2024 | Lake Nacimiento at main marina launch | General awareness | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Jun 28, 2024 | Lake Nacimiento at day use area | General awareness | Updates from routine monitoring program-organization |
| Jun 28, 2024 | Lake Nacimiento at main marina launch | None | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| May 21, 2024 | Lake Nacimiento at day use area | General awareness | Updates from routine monitoring program-organization |
| May 21, 2024 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| May 21, 2024 | Lake Nacimiento at main marina launch | None | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| May 21, 2024 | Lake Nacimiento at main marina launch | None | Suspected bloom, investigation ongoing |
| Aug 31, 2023 | Lake Nacimiento at main marina launch | General awareness | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Jun 29, 2023 | Lake Nacimiento at main marina launch | NA - refer to Report Details | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Jun 29, 2023 | Lake Nacimiento at day use area | NA - refer to Report Details | Rec general awareness; Updates from routine monitoring program-organization |
| May 25, 2023 | Lake Nacimiento at day use area | NA - refer to Report Details | Rec general awareness; Updates from routine monitoring program-organization |
| May 25, 2023 | Lake Nacimiento at main marina launch | NA - refer to Report Details | Rec algal mat general awareness; Updates from routine monitoring program-organization |
| Dec 9, 2022 | Lake Nacimiento at main marina launch | None | Updates from routine monitoring program-organization |
| Dec 9, 2022 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| Nov 28, 2022 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| Nov 28, 2022 | Lake Nacimiento at main marina launch | None | Updates from routine monitoring program-organization |
| Oct 19, 2022 | Lake Nacimiento at main marina launch | None | Updates from routine monitoring program-organization |
| Oct 19, 2022 | Lake Nacimiento at main marina launch | General awareness | Rec general awareness |
| Sep 1, 2022 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| Sep 1, 2022 | Lake Nacimiento at main marina launch | NA - refer to Report Details | Rec general awareness |
| Sep 1, 2022 | Lake Nacimiento at day use area | NA - refer to Report Details | Posted general awareness |
| Jun 30, 2022 | Lake Nacimiento at day use area | None | Updates from routine monitoring program-organization |
| Jun 30, 2022 | Lake Nacimiento at main marina launch | None | Updates from routine monitoring program-organization |
| May 27, 2022 | Lake Nacimiento at main marina launch | None | Updates from routine monitoring program-organization |
| May 27, 2021 | Spot not described | None | Testing results below posting triggers |
| Sep 3, 2020 | Lake Nacimiento | NA - refer to Report Details |
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.