Lake Piru: toxic algae advisories
Lake Piru, Los Angeles County. See all Los Angeles County waters.
What the state's records say
The state's latest record, from May 25, 2021, 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 Lake Piru
The state's latest record, from May 25, 2021, recommends no advisory. For Lake Piru, 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 May 2, 2026: about 110,000 cells/mL of cyanobacteria near the center of Lake Piru.
A satellite estimate from EPA CyAN for a 4.9 km² lake. It does not measure toxins and does not change the advisory status.
| Week ending | Estimate |
|---|---|
| May 2, 2026 | about 110,000 cells/mL |
| Apr 25, 2026 | about 260,000 cells/mL |
| Apr 18, 2026 | about 840,000 cells/mL |
| Apr 11, 2026 | about 890,000 cells/mL |
| Apr 4, 2026 | about 460,000 cells/mL |
| Mar 28, 2026 | about 340,000 cells/mL |
| Mar 21, 2026 | about 49,000 cells/mL |
| Dec 14, 2024 | about 110,000 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 |
|---|---|
| near swim beach | The state's latest record, from May 25, 2021, recommends no advisory. |
Advisory history
Every advisory record the state has published for Lake Piru, 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 |
|---|---|---|---|
| May 25, 2021 | near swim beach | None | Testing results below posting triggers |
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.