Incoming rainfall could lead to heightened levels of E. coli in the Shenandoah River.

In the past year, Wayne Webb, a director of the Lord Fairfax Soil and Water Conservation District and a retired water quality specialist with the U.S. Geological Survey, has been looking into water quality data from the Virginia Department of Environmental Quality and the Friends of the Shenandoah River. (Webb is also the research manager of the Friends of the Shenandoah River.)

In an analysis, Webb said that E. coli levels have tended to be too high for people to swim in nearby tributaries of the Shenandoah River at all times and in the river following rainfall events. Otherwise, he said, the levels have been low enough for swimming.

“What is true about the river is that it always exceeds drinking water standards,” Webb said. “It exceeds swimming standards after rainfall events. So when the flow gets high, the rivers are going to exceed the standards for swimming.”

The Virginia Department of Health, for its part, urges people not to swim along ocean beaches for a few days after rainfall.

“Bacteria levels are likely to be high, and disease-causing organisms are likely to be present after rainfall due to pollution from land runoff and other sources,” the department states.

Webb said the same thing applies for rivers. The Lord Fairfax Health District, part of the Department of Health, has not responded to a request for comment.

For several years, environmental groups have argued that E. coli levels throughout the Shenandoah River are too high. Last year, the Environmental Integrity Project, an environmental nonprofit out of Washington, D.C., released a report stating that 91 percent of locations in the Shenandoah River saw E. coli levels that exceeded state standards.

That report argued that livestock were major contributors to the high levels because some animals have defecated into the river and because of water runoff in areas that are fertilized with manure.

Tom Pelton, the executive director for the Environmental Integrity Project, said that the report showed widespread problems in E. coli levels throughout the river.

“We looked at all of the segments (of the river),” Pelton said. “As you can see, a large number of them are impaired.”

But for Webb, the bigger lesson in the data is that the levels tend to exceed swimming standards following rainfall and near tributaries.

To Webb, that data suggests that any high E. coli levels downstream in the river appear to come from water runoff.

“The E. coli, they get [in the river] because they’re washed off the land, not because of cattle defecation in the river,” Webb said.

Webb added that in the tributaries, cattle defecation likely has led to heightened E. coli levels.

“In the little streams, it’s a different story because [the streams] don’t dilute as much and the cattle per cubic foot per second are higher, so they can push the E. coli counts above the swimming standard,” Webb said.

Webb argued that the river is relatively safe when the water flow levels are not high because of rainfall events. But he also urged caution.

“You’ve got to be careful,” Webb said. “You don’t drink the water; you don’t go in with big cuts on your legs and stuff like that.”