Environmental experts warned Foggy Bottom residents Tuesday that D.C.’s water supply could soon be contaminated by a hydraulic fracking project two states away.

Fracking, which allows for deep drilling into shale reserves, can allow toxins to seep into city water supplies, said Dusty Horwitt, a senior analyst for nonprofit organization Earthworks.

Horwitt told about 20 Foggy Bottom locals that the city’s water supply could be at risk because if the U.S. Forest Service allows a fracking project to begin in a West Virginia national forest later this month.

That forest, called the George Washington National Forest, sits at the top of the Potomac Watershed, which would mean polluted runoff would spill into the source of D.C.’s water.

“It would be a big victory if we could convince the Forest Service not to adopt fracking in next year’s plan.” Horwitt said. “It is not a wise decision to allow fracking until more information can come out about how to do this process safely.”

Three local water and sewer organizations, including D.C. Water, Fairfax Water and Washington Aqueduct, have pushed the U.S. Forest Service not to approve the drilling, which pushes sand, water and toxic chemicals into reserves to release natural gas.

It’s also been heralded as a way to decrease America’s reliance on coal and oil.

Horwitt added that fracking in West Virginia could impact the water supply of at least 4 million Washington-area residents.

Jessica Edwards-Brant, an employee of D.C. Water, said fracking is dangerous because “there are so many unknowns with fracking,” pointing to the lack of government oversight and fracking’s exemption from the Clean Water Act.