UPDATED: Algae blooms affect Lake Anne, Thoreau and Audubon in Reston

Updated at 3:40 p.m. — An algae bloom was spotted this morning in Lake Anne,  joining blooms on Lake Thoreau and Lake Audubon, Reston Association says.

“At this time, Reston Association has determined that treatment of the blooms would not be beneficial, as a mass die-off of algae after treatment would cause a dip in otherwise healthy oxygen levels, therefore posing significant risk to fish and wildlife in the lake,” the organization said, advising residents and pets to avoid contact with the affected lakes.

Earlier: Reston Association plans to let algae blooms at Lake Thoreau and Lake Audubon run their natural course.

In response to concerns from the community about the blooms, RA said that treating them could disrupt oxygen levels in the lakes, putting fish and wildlife at risk.

“While we understand concerns about the algae bloom, especially this late in the season, our experts believe that leaving the bloom to run its course is more likely to result in a balanced outcome,” RA wrote in a statement on social media.

RA says it will continue to monitor the situation.

RA confirmed to FFXnow that the blooms are the same ones that emerged in mid-October. At the time, the scope of the bloom on Lake Thoreau was limited, but it contained potentially harmful cyanobacteria, leading RA to advise avoiding contact with the water.

“These blooms arrived quickly at the onset of fall turnover, which mobilizes nutrients from the bottom of the lake into the rest of the water column,” said Cara O’Donnell, RA’s director of communications and community engagement. “Typically, a fall turnover bloom like this would subside quickly, but we’ve had unseasonably warm weather this fall that is causing the bloom to linger longer than anticipated.”

Lake Audubon also had a bloom this summer that was cleared in August.

Our watershed team is closely monitoring the situation, and at this time they’ve chosen to hold off on a late-season treatment out of concern for the health of fish and wildlife in and around the lake. pic.twitter.com/h7VDn6TcIN

— Reston Association (@RestonOnline) November 15, 2023