After learning of potentially harmful algae blooms in the Shenandoah River near Strasburg, the Health Department is cautioning people not to swim in that area until the results of an algae test come in later this week.

Algae, itself, is not uncommon in the river and is usually harmless, said Dr. Colin Greene, director of the Lord Fairfax Health District.

But the algae blooms discovered at the Bethal Road area of Strasburg could be cyanobacteria, which he said “has the ability to put out a neurotoxin.”

The threat comes from swallowing algae-tainted water, so he asked people not to swim or let their animals drink from that area of the river until the results are announced. He expects answers as soon as Thursday.

“Swimming in the river is not generally the greatest idea anyhow,” Greene said.

Except in especially calm water, he said areas of moving water can be dangerous.

“People drown in rivers,” he said. “The currents surprise them and [currents] can change.”

Though people could use boats or tubes down the river, Greene said visitors might rethink swimming in its waters.

“The Shenandoah unfortunately is polluted,” Greene said.

The Shenandoah’s slow-moving pace and agricultural setting make it susceptible to sediment and runoff from area farms, which provoke algae, said Mike Selckmann, senior aquatic ecologist at the Interstate Commission on the Potomac River Basin.

Phosphorous binds to sediment, he said, and the plants feed off of that.

This makes the Shenandoah “kind of a good candidate to cause algae blooms,” Selckmann said.

He said his office, along with the Department of Environmental Quality, has been researching reasons why algae has been forming in particular “hot spots” along the Shenandoah, such as Strasburg.

If results this week come back clean, Greene said the Health Department will lift its warning, and if not then it will provide further information.

For those who do go out on the river, Greene said that algae will likely not be a concern for much longer this season.

“Generally these things pass,” he said.

“This is not permanent damage to the river we’re talking about. These algae blooms come and go.”

For the next three days, though, he recommended caution.

“Don’t swim,” he said. Instead, “get out your canoe.”

The Health Department also recently published a report of cyanobacteria on Lake Anna: vdh.virginia.gov/content/uploads/sites/178/2021/06/LA-HAB-Report-6.30.21.pdf

Contact Josette Keelor at jkeelor@nvdaily.com