Harmful algal blooms now detected at two South Lake Tahoe beaches

SOUTH LAKE TAHOE, Calif. - Samples of water collected at both Regan Beach and El Dorado Beach in South Lake Tahoe have detected Anatoxin-a present, prompting caution advisories to be issued. Signs are being placed at both beaches to alert the public of the possible dangers should animals drink the affected water, of if people swim in the area.

Regan Beach

At Regan Beach, samples of water taken on September 30, 2021 detected a low level of the toxin which came with a caution, then a retest on October 7 moved the caution level to "advisory recommended."

The level of the algal Anatoxin-a was present at 0.27 ug/L during the second test.

On July 12, Regional Water Board staff sampled Regan Beach due to wash up of algae on the beach. The sample contained a moderate amount of the cyanobactera species Brasilonema, but no other cyanobacteria were observed at that time, and no toxins were detected.

The City of South Lake Tahoe closed the gates at Regan Beach so no vehicles and passengers would drive to the shoreline in question. Lahontan said they only asked the caution sign to be posted, but the City, out of an abundance of caution, chose to close it.

El Dorado Beach

Water Board staff collected a sample of water from El Dorado Beach on October 7, 2021. The report on that sample became available on October 14, showing Anatoxin-a was detected at 0.23 ug/L.

Drinking water is considered safe with a level of Anatoxin-a at .10 ug/L.

The City cannot close El Dorado Beach as easily as Regan Beach but they are looking at ways to better inform the public in the area.

The advisory recommendations for both beaches: Stay away from algae and scum in the water. Do NOT let pets go in the water, drink the water, or eat scum on the shore. Keep Children away from algae. Do not eat shellfish from this waterbody.

There will be follow up testing to ensure no more health risks exist. The Anatoxin-a is normally present in the environment, but the current levels are the reason for the warnings.

There are several bodies of water in the state that have caution levels due to detected toxins, all the way up to warning levels of toxins. The two South Lake Tahoe beaches are the only two in El Dorado County, Alpine County has no positive tests, one in Placer County (Duncan Creek) and three in Mono County (Long Lake, Ruby Lake, West Walker River at the Leavitt Meadow Trail).

Algal blooms an emerging threat to clear lakes worldwide, though they aren't all toxic. These filamentous algal blooms, known as FABs, need lots of light, so they occur at lake edges where people want to swim and play, said a recent report by the University of Nevada, Reno. Anatoxin-a occurs naturally and may be present when a harmful algal bloom has formed on a lake, pond, or stream. Not all algal blooms contain the cyanobacteria that produce anatoxin-a. However, there is no clear way to know if an algal bloom contains harmful toxins.