Prosser Creek Reservoir: toxic algae advisories
Prosser Creek 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 Prosser Creek Reservoir
The state's latest record, from Oct 7, 2026, recommends no advisory. For Prosser Creek 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 Nov 29, 2025: about 230,000 cells/mL of cyanobacteria near the center of Prosser Creek Reservoir.
A satellite estimate from EPA CyAN for a 2.9 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| Nov 29, 2025 | about 230,000 cells/mL |
| Nov 8, 2025 | about 17,000 cells/mL |
| Nov 1, 2025 | about 16,000 cells/mL |
| Jan 11, 2025 | about 120,000 cells/mL |
| Apr 27, 2024 | about 110,000 cells/mL |
| Apr 20, 2024 | about 120,000 cells/mL |
| Mar 16, 2024 | about 82,000 cells/mL |
| Dec 2, 2023 | about 13,000 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 |
|---|---|
| Lakeside Campground | The state's latest record, from Oct 7, 2026, recommends no advisory. |
| Marina | The state's latest record, from Oct 19, 2023, recommends no advisory. |
| Lakeside Campground | The state's latest record, from Aug 17, 2022, recommends no advisory. |
| Boat Ramp | The state's latest record, from Jun 3, 2022, recommends no advisory. |
Advisory history
Every advisory record the state has published for Prosser Creek 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 | Lakeside Campground | None | Advisory based on visual and toxins |
| Oct 7, 2026 | Lakeside Campground | None | Advisory based on visual and toxins |
| Jun 24, 2026 | Lakeside Campground | None | Advisory based on visual and toxins |
| Oct 2, 2025 | Lakeside Campground | None | Confirmed no bloom |
| Aug 22, 2025 | Lakeside Campground | None | Testing results below posting triggers |
| Jun 26, 2025 | Lakeside Campground | None | Testing results below posting triggers |
| Oct 9, 2024 | Lakeside Campground | None | Updates from routine monitoring program-organization |
| Aug 28, 2024 | Lakeside Campground | None | Updates from routine monitoring program-organization |
| Jun 26, 2024 | Lakeside Campground | None | Updates from routine monitoring program-organization |
| Oct 19, 2023 | Marina | None | Updates from routine monitoring program-organization |
| Oct 19, 2023 | Lakeside Campground | None | Updates from routine monitoring program-organization |
| Aug 28, 2023 | Lakeside Campground | None | Updates from routine monitoring program-organization |
| Jul 5, 2023 | Lakeside Campground | None | Updates from routine monitoring program-organization |
| Jul 5, 2023 | Marina | None | Updates from routine monitoring program-organization |
| Aug 17, 2022 | Lakeside Campground | None | visual monitoring based advisory |
| Jun 23, 2022 | Lakeside Campground | None | Testing results below posting triggers |
| Jun 3, 2022 | Boat Ramp | None | Advisory based on visual and toxins |
| Jun 3, 2022 | Lakeside 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.