Toxic algae prompts warning at Lake Mead

The National Park Service is warning people to stay out of the water in parts of Lake Mead National Recreation Area now being colonized by a potentially toxic algae.

The blue-green growth has turned up at several popular areas of Lake Mead and Lake Mohave.

Park spokeswoman Christie Vanover said officials have been monitoring the algae since it was first spotted early last month. It wasn’t considered a concern until this week, when tests came back showing low levels of microcystin, a toxin produced by the algae, in water samples taken near Las Vegas Boat Harbor, the park’s busiest marina.

Samples collected in Las Vegas Bay and from an area just upstream from Hoover Dam also showed low levels of the toxin.

No areas have been closed to the public, but as a precaution, park officials are warning visitors not to swim, water ski or jet ski in areas where the algae can be seen.

People should also keep their pets out of the water and avoid touching residue on the shoreline or filling water tanks anywhere the algae is present.

Anyone who comes into contact with the algae should rinse thoroughly with clean water.

Drinking untreated water from the lake is never a good idea, algae or not.

Lake Mead supplies roughly 90 percent of the drinking water used in the Las Vegas Valley, but the algae poses no threat to water customers, said Bronson Mack, spokesman for the Southern Nevada Water Authority.

The chlorine and ozone treatments the authority already uses will destroy any of the algae or microcystin that may find their way into the agency’s intake pipes at the lake.

Mack said the authority has been sampling the water at and around its intakes and its two treatment plants since traces of a toxin first turned up in the lake late Tuesday.

“We haven’t detected it at our treatment facilities, and even if we did we have advanced treatment methods that do eliminate it,” he said.

Health issues related to microcystin range from rashes and skin irritations to gastrointestinal illness.

Vanover said the National Park Service, the water authority and the Nevada Division of Environmental Protection will continue to monitor the situation.

She said the algae is so widespread that it can be seen from the air, but Mack said what is happening now still doesn’t qualify as a “full bloom” like the one that turned Lake Mead green in 2001.

There’s nothing terribly exotic about the type of algae now growing in the lake. Mack said this variety usually pops up in autumn and then dies in the winter when the water cools off.

Relatively mild conditions this winter may have allowed the algae to hang on until now.

Another possible culprit is the low level of the lake itself, which can lead to higher water temperatures and greater concentrations of the nutrients algae feeds on.

“It’s possible, but I can’t say with any certainly,” Mack said.

Contact Henry Brean at hbrean@reviewjournal.com or 702-383-0350. Follow @RefriedBrean on Twitter.