Residents told to stay out of Lake Thoreau after algae bloom appears

An algae bloom has taken over a portion of Reston’s Lake Thoreau.

In a statement released yesterday (Tuesday), Reston Association said the bloom contains “potentially harmful cyanobacteria.”

“It is advised for residents and their animals to avoid contact with the water at this time and remain attentive to any signage posted around the lake,” RA wrote.

Cyanobacteria are microscopic organisms found in all types of water, according to the Centers for Disease Control and Prevention. Harmful cyanobacteria can produce toxins and block sunlight that other organisms need to live.

As of earlier this morning (Wednesday), the bloom was limited, according a spokesperson for RA. The association expects to determine if the bloom is expanding or shrinking today.

“With the cooling temperatures, we don’t anticipate treatment will be necessary; however, if the bloom lingers, we will consider treatment options,” Cara O’Donnell, RA’s spokesperson, said.

There are currently no restrictions on boating or fishing, but residents are encouraged to wash any areas that have direct contact with the lake.

When the bloom subsides, signage will be removed.

Reston typically sees a couple of cases of algae blooms every summer. Algae spotted in Lake Audubon in early August was deemed potentially harmful, fueled by a water main break that also killed some fish in Snakeden Branch stream.

It is advised for residents and their animals to avoid contact with the water at this time and remain attentive to any signage posted around the lake.

— Reston Association (@RestonOnline) October 10, 2023