Algae expert talks about recent bloom

The most recent harmful algae blooms on Lake Anna were a hot topic at the Lake Anna Civic Association’s annual membership meeting on July 27 at the North Anna Nuclear Information Center. 

Margaret Smigo, waterborne hazards program coordinator for the Virginia Department of Health, was the guest speaker.  

“The algae bloom is a symptom of a larger problem,” she said.   

Her agency issued a no-swim advisory for portions of the lake in mid-July after high concentrations of cyanobacteria were found in the Upper and Middle Pamunkey branches and the Middle and Lower North Anna branches. 

“We issued the advisory because of the health risks and we want people to be aware that the toxics may be present,” she said. “With a body of water the size of Lake Anna, it is hard to pinpoint an exact spot so the advisory encompasses a larger area.”

Exposure to cyanobacteria can cause skin rash and gastrointestinal illnesses, such as upset stomach; nausea; vomiting and diarrhea, particularly in young children, the elderly and those with compromised immune systems. Animals, especially dogs, can also be impacted by exposure, Smigo said.

During her presentation, Smigo explained that a “bloom” occurs when there is a high density of phytoplankton in the area. The phytoplankton occur naturally in water bodies but when there is a bloom it means there is a high level of the bacteria in one area and something in the environment is driving their growth.

“There are over 73,000 species of algae and about 300 of them will form blooms,” she said. “Of those 300 species, less than 100 produce toxins as part of their life cycle.”

When asked what causes the blooms, Smigo said there were several things that change the environment, allowing the algae to grow rapidly. A favorable environment includes such things as warmer water temperature and lots of sunlight, an influx of nutrients due to rain and runoff events, and mixing of the water columns which stirs up nutrients from the sediment.

“Lake Anna is pretty much an open pond where sunlight hits a majority of the surface during the day,” Smigo said. “There is shade around the shoreline, but the main surface area is open. The addition of boat traffic which stirs up the water also helps to create a favorable environment.”

Harmful algae blooms occur across the country and are not isolated to Lake Anna, Smigo said. However, in Virginia Lake Anna has experienced the largest algae event this year.

The health department tested various locations where a bloom was observed.  When one tested positive, everything upstream was included in the advisory.

“The bloom doesn’t stay put in one area, it moves with the water currents as boats travel through it and wake actions run across the surface,” she said.

Typically, an advisory is lifted after two consecutive samplings where results are below the threshold. However, Smigo said the task force is considering other parameters for Lake Anna.

“We can lift advisories based on the history of water quality and weather events as well,” she said. “So, if we look at all the factors and feel it’s safe to lift the advisory after one round of tests, we will.”

While there is currently an advisory on the lake, Smigo said the blooms this year have not reached the toxin levels that occurred in 2018.  Testing has occurred monthly above the Route 208 bridge since April, but will now be conducted every two weeks.

The Virginia Department of Environmental Quality was scheduled to conduct another round on testing on July 30 with results available in about a week. To check those results and to see any advisories, Smigo encouraged those in attendance to visit the health department’s website at

All recent advisories and a map of algae hotspots are on the site. Residents can even plug in their addresses to see if their property is included. They can also report potential blooms on the site and attach photos.  

If residents suspect they have developed an illness due to exposure, they should call the harmful algae hotline at (888) 238-6154, Smigo said.  

Smigo said she was not aware of any illnesses that have been attributed to the lake’s algae issues.

“There are lots of other algae and bacteria living in Lake Anna as well, so it is difficult to determine the exact cause,” she said.