Lake Berryessa: toxic algae advisories
Lake Berryessa, Napa County. See all Napa County waters.
What the state's records say
Caution advisory, last posted Aug 28, 2026. No all-clear recorded.
4 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: Algae that can make toxins may be present. Keep people, children and pets away from algae and scum, and do not let pets drink the water.
Before you go, check the state's official algae page and any signs posted at the water.
Dogs at Lake Berryessa
The state has an advisory on file for Lake Berryessa (Caution advisory), last posted Aug 28, 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 Apr 30, 2022: about 110,000 cells/mL of cyanobacteria near the center of Lake Berryessa.
A satellite estimate from EPA CyAN for a 64.2 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Apr 30, 2022 | about 110,000 cells/mL |
| Apr 9, 2022 | about 18,000 cells/mL |
| Oct 2, 2021 | about 41,000 cells/mL |
| Sep 25, 2021 | about 61,000 cells/mL |
| Jan 2, 2021 | about 13,000 cells/mL |
| Feb 15, 2020 | about 11,000 cells/mL |
| Feb 8, 2020 | about 9,300 cells/mL |
| Jan 11, 2020 | about 7,900 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 |
|---|---|
| Markley Cove | Reports on file, with no advisory level the state has classified. |
| Oaks day use area acorn beach | Caution advisory, last posted Aug 28, 2026. No all-clear recorded. |
| Putah Canyon campground | Caution advisory, last posted Aug 28, 2026. No all-clear recorded. |
| Spanish flat campground | The state's latest record, from Jun 30, 2022, recommends no advisory. |
| Spanish flat day use area | The state's latest record, from Jun 30, 2022, recommends no advisory. |
| East of Marcly cove marina | The state's latest record, from Jun 30, 2022, recommends no advisory. |
| a bit south of the bridge | Caution advisory, last posted May 20, 2022. No all-clear recorded. |
| Lake Berryessa - Smittle Creek Trailhead | The state's latest record, from May 8, 2020, recommends no advisory. |
| Lake Berryessa Oak Shores Day Use Area Coyote Swim Beach | Caution advisory, last posted Aug 31, 2018. No all-clear recorded. |
| Lake Berryessa - Markley Canyon Arm (coves along shoreline) | The state's latest record, from May 11, 2018, recommends no advisory. |
Advisory history
Every advisory record the state has published for Lake Berryessa, 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 |
|---|---|---|---|
| Aug 28, 2026 | Markley Cove | NA - refer to Report Details | Suspected illness reported; Testing results below posting triggers |
| Aug 28, 2026 | Oaks day use area acorn beach | Caution | visual monitoring based advisory |
| Aug 28, 2026 | Putah Canyon campground | Caution | visual monitoring based advisory |
| Aug 5, 2026 | Markley Cove | NA - refer to Report Details | Suspected illness reported |
| Jul 2, 2026 | Oaks day use area acorn beach | General awareness | Updates from routine monitoring program-organization |
| Jul 2, 2026 | Putah Canyon campground | General awareness | Updates from routine monitoring program-organization |
| Jun 30, 2022 | Spanish flat campground | None | No cyano, other algae present. |
| Jun 30, 2022 | Spanish flat day use area | None | No cyano, other algae present. |
| Jun 30, 2022 | Oaks day use area acorn beach | None | No cyano, other algae present. |
| Jun 30, 2022 | Oaks day use area acorn beach | None | No cyano, other algae present. |
| Jun 30, 2022 | East of Marcly cove marina | None | No cyano, other algae present. |
| May 20, 2022 | a bit south of the bridge | Caution | Suspected illness reported |
| May 8, 2020 | Lake Berryessa - Smittle Creek Trailhead | None | De-posting advisory. |
| Aug 31, 2018 | Lake Berryessa Oak Shores Day Use Area Coyote Swim Beach | Caution | |
| May 11, 2018 | Lake Berryessa - Markley Canyon Arm (coves along shoreline) | None |
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.