The Reston Association, led by CEO Peter Lusk, posted warning signs at Lake Anne access points on Wednesday, Oct. 14, after residents reported clumps of potentially harmful algae floating on the water's surface.

Boating is still allowed. But the association is urging residents and visitors to avoid contact with the water wherever algae is visible, according to an advisory on the Reston Association website. Green or blue-green discoloration is more likely to contain toxins, the association notes on its Lakes & Watersheds page.

The association said its primary concern is dogs ingesting the algae, and it urged pet owners to take extra precautions around the lake.

The Oct. 14 advisory did not identify the specific algae species or say how long the warning will remain in place. The association said it will continue to monitor conditions and provide updates.

This is the second algae alert at Lake Anne this year. In July, the association's watershed team discovered small clumps of cyanobacteria, a type of blue-green algae, during routine weekly monitoring of the lake. That earlier bloom led to a temporary suspension of stand-up paddleboard rentals, according to a separate Reston Association notice.

The July notice also advised residents to rinse off as soon as possible if they or a pet came in contact with lake water, since the primary risk comes from ingestion and direct contact with algae clumps. The Oct. 14 advisory did not mention any new restrictions on paddleboard or other watercraft rentals.

The association runs weekly monitoring on its lakes. Reston's four man-made lakes cover 125 acres and draw residents for fishing, boating, wildlife watching and lakeside picnicking. Swimming is prohibited in all four: Lake Anne, Lake Thoreau, Lake Audubon and Lake Newport.

Residents who spot algae blooms can email the Reston Association Watershed Department. Anyone who experiences health effects after contact with a bloom can call the Virginia Harmful Algal Bloom Hotline at 888-238-6154.