Virginia Health Department signs warning of algae blooms are still visible at Strasburg Town Park.

Tropical Storm Ida helped clear the harmful algae from the North Fork of the Shenandoah River last week, a state expert said Thursday.

But state health officials have not yet lifted an advisory warning people to stay clear of the harmful algae bloom along more than 50 miles of the river, from Woodstock to Front Royal.

The Lord Fairfax Health Department issued the advisory earlier this summer with updates as the algae spread, warning people to not go into the river and not to let animals near or drink the water because exposure to the algae bloom can cause health problems.

The health department had not lifted or changed the advisory as of late Thursday afternoon.

The Friends of the Shenandoah River regularly monitors waterways in the region and reports its findings to the Virginia Department of Environmental Quality, which the state agency uses in its work. Tara Wyrick, water quality and assessment manager at the DEQ’s regional Harrisonburg office, spoke by phone Thursday about the recent findings.

Volunteers with the organization, who the DEQ referred to as citizen scientists, monitored the river in Strasburg on Sept. 2 and sent photographs to the state agency, Wyrick said. The images showed the river at a high level with turbid waters shortly after the rain from Ida, she said.

Scientists from the DEQ regional office in Harrisonburg collected water samples on Tuesday.

“The samples themselves take a couple of days to process but our field observations indicated very high flows,” Wyrick said. “The turbidity, which is the cloudiness of the water, had subsided a bit so last week the photos we saw kinda looked like chocolate milk — very, very cloudy.

“You couldn’t see the bottom,” Wyrick said. “You couldn’t see more than a couple of inches through the water, if that, whereas our observations on Tuesday ... showed us that the sediment and suspended solids were settling out, the water was clearer.”

DEQ scientists saw “hardly any presence of algae” at the testing sites, Wyrick. They did see submerged, aquatic vegetation — plants rooted at the bottom of the river and part of the life cycle of the waterway.

“They are a natural presence,” Wyrick said. “They provide habitat for fish and the nutrient invertebrates that provide the basis for the food chain.

“So we saw some of those ‘cause they’re super hardy ... rooted into the river bottom,” Wyrick said.

But high river levels and fast-flowing water can carry away the algae species that scientists observed, Wyrick said.

The DEQ passes on its testing results and observations to the Virginia Department of Health, which then decides whether or not to lift the advisory.

– Contact Alex Bridges at abridges@nvdaily.com