Boca Reservoir: toxic algae advisories
Boca Reservoir, Nevada County. See all Nevada County waters.
What the state's records say
The state's latest record, from Oct 7, 2026, recommends no advisory.
That reflects what the state knew on that date. It is not a finding that the water is safe now: blooms can return within days, and many are never reported.
Before you go, check the state's official algae page and any signs posted at the water.
Dogs at Boca Reservoir
The state's latest record, from Oct 7, 2026, recommends no advisory. For Boca Reservoir, that is not the same as an all-clear for today. Look at the water before your dog goes in: keep it out of green, blue-green or scummy water and away from mats on the shore.
Satellite estimate (not an advisory)
Week ending Jul 4, 2026: about 6,500 cells/mL of cyanobacteria near the center of Boca Reservoir.
A satellite estimate from EPA CyAN for a 3.9 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Jul 4, 2026 | about 6,500 cells/mL |
| Feb 1, 2025 | about 78,000 cells/mL |
| Jun 15, 2024 | about 45,000 cells/mL |
| Jan 6, 2024 | about 56,000 cells/mL |
| Dec 30, 2023 | about 97,000 cells/mL |
| Dec 16, 2023 | about 110,000 cells/mL |
| Dec 2, 2023 | about 670,000 cells/mL |
| Nov 18, 2023 | about 300,000 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 |
|---|---|
| Last Pullout Before Boca Rest Campground | The state's latest record, from Oct 7, 2026, recommends no advisory. |
| Last Pullout Before Boca Rest Campground | The state's latest record, from Aug 17, 2022, recommends no advisory. |
Advisory history
Every advisory record the state has published for Boca Reservoir, 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 |
|---|---|---|---|
| Oct 7, 2026 | Last Pullout Before Boca Rest Campground | None | Advisory based on visual and toxins; Confirmed no bloom |
| Sep 3, 2026 | Last Pullout Before Boca Rest Campground | None | Advisory based on visual and toxins; Confirmed no bloom |
| Jun 24, 2026 | Last Pullout Before Boca Rest Campground | None | Advisory based on visual and toxins; Confirmed no bloom |
| Oct 2, 2025 | Last Pullout Before Boca Rest Campground | None | Advisory based on visual and toxins; Confirmed no bloom |
| Aug 22, 2025 | Last Pullout Before Boca Rest Campground | None | Advisory based on visual and toxins |
| Jun 26, 2025 | Last Pullout Before Boca Rest Campground | None | Advisory based on visual and toxins |
| Oct 9, 2024 | Last Pullout Before Boca Rest Campground | None | Advisory based on visual and toxins |
| Aug 28, 2024 | Last Pullout Before Boca Rest Campground | None | Updates from routine monitoring program-organization |
| Jun 26, 2024 | Last Pullout Before Boca Rest Campground | None | Updates from routine monitoring program-organization |
| Oct 19, 2023 | Last Pullout Before Boca Rest Campground | None | Updates from routine monitoring program-organization |
| Aug 28, 2023 | Last Pullout Before Boca Rest Campground | None | Updates from routine monitoring program-organization |
| Jul 5, 2023 | Last Pullout Before Boca Rest Campground | None | Updates from routine monitoring program-organization |
| Aug 17, 2022 | Last Pullout Before Boca Rest Campground | None | visual monitoring based advisory |
| Jun 23, 2022 | Last Pullout Before Boca Rest Campground | None | No cyano, other algae present. |
| Jun 3, 2022 | Last Pullout Before Boca Rest Campground | None | Advisory based on visual and toxins |
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.