For the second straight year, the Virginia Department of Health has advised people to avoid swimming in certain areas of Lake Anna due to a harmful algae bloom.
The areas the state agency identified on July 16 include the Upper and Middle Pamunkey branches and the Middle and Lower North Anna branches. These are sections of the lake targeted for algae testing earlier this year.
Some harmful algae, called cyanobacteria, can cause skin rash and gastrointestinal illnesses, such as upset stomach, nausea, vomiting and diarrhea.
“Algae blooms can occur when warm water and nutrients combine to make conditions favorable for algae growth,” Lorrie Andrew-Spear, a health department spokesperson, said in a prepared statement. “Most algae species are harmless; however, some species may produce irritating compounds or toxins.”
She advised people to avoid “discolored water or scums that are green or bluish-green, because they are more likely to contain toxins.”
The algae that led to the state advisory was collected from lake water samples on July 10. The health department is posting advisory signs within the affected areas. More testing is planned during the last week of July, weather permitting.
Last August and September, potentially dangerous algae was discovered in the same areas of the upper lake and in the waste heat treatment facility. The problem triggered a dialogue among state and local officials and lake advocates about possible causes and solutions.
Margaret Smigo, a waterborne hazards specialist for the health department, said at a Lake Anna Civic Association meeting in November that changes in algae levels can be caused by an influx of nutrients, typically from runoff from the surrounding land. The nutrients may include fertilizers and animal wastes. Algae can also be triggered by changes in temperature and light availability.
“Typically, the presence of a bloom is determined when the dissolved oxygen levels [in water] rise during the day and drop at night,” Smigo said.
Specific locations where the water was tested for algae include a site near Days Bridge Road (Rt. 719) at the Spotsylvania County line. Two others are on the same route near The Cove at Lake Anna and at Terrys Run, while a fourth is in Pamunkey Creek above Terrys Run.
While those sites yielded cyanobacteria concentrations above safe levels, other tests showed harmless amounts at the Route 208 bridge, near Lake Anna State Park and at the popular gathering spot called the “Sandbar.”