Lago Los Osos: toxic algae advisories

Lago Los Osos, Alameda County. See all Alameda County waters.

What the state's records say

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 Lago Los Osos

The state has an advisory on file for Lago Los Osos (Caution advisory), last posted Oct 9, 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.

More on dogs and toxic algae.

Reported spots

The state records each report at a spot, such as a beach or a boat ramp. Each spot's latest deciding record:

Advisory history

Every advisory record the state has published for Lago Los Osos, newest first. "None" is the state's record that no advisory was recommended on that date. "NA" records do not change a status.

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.