'Danger' Advisories Issued Due To Toxic Algae In Several East Bay Lakes

CASTRO VALLEY, CA — Bay Area residents planning to spend time at East Bay Regional Park lakes over the Labor Day weekend may be disappointed.

If heading to an East Bay park, note that swimming might not be an option, as "danger" advisories are in place for several lakes due to the lingering presence of blue-green algae, also known as cyanobacteria.

"The advisories typically transition up and down throughout the year based on many factors, ranging from no advisory, caution, or danger," said Dave Mason, public information supervisor of the East Bay Regional Park District.

"Danger" advisories have been issued for Lago Los Osos and Horseshoe Lake / Niles Swim Beach at Quarry Lakes Regional Park; the Martinez Shoreline at Radke Martinez Regional Shoreline Park; Del Valle East Swim Beach at Del Valle Regional Park; the Contra Loma Reservoir at Contra Loma Regional Park. Some of the danger-level advisories have been active throughout the summer, such as at Contra Loma, while others, like Del Valle East Beach, rose to the danger level this month.

The "advisory" warns that "toxins from algae in this water can harm people and animals." Specifics of the advisory include staying out of the water and not touching "scum in the water or on the shore"; not drinking the water or using it for cooking; and not allowing pets to go into or drink the water due to its toxicity, according to park officials.

"Certain conditions – low water levels, limited water circulation, increased temperature and light, among other factors – can cause blue-green algae to bloom and, in some cases, release toxins," stated park officials. "Scientists do not know what causes the blue-green algae to become toxic."

The East Bay Regional Park District had its first-ever toxic algae bloom in 2014, they said.

Red signs are currently posted in the above-mentioned parks, in proximity to the lakes, to alert visitors to the presence of blue-green algae.

To stay updated on the "Current Water Quality Conditions" of East Bay lakes, go here.

A PDF brochure about blue-green algae, courtesy of the East Bay Regional Park District, is available here.