For more than a century, the U.S. Navy has been using the Potomac River to test weapons, each year firing thousands of projectiles and bullets into the water, and detonating hundreds explosives, roughly 50 miles downstream of Washington D.C. The Navy is conducting this testing illegally, potentially harming the river’s ecosystems, according to a lawsuit filed this week by two environmental groups.

The Naval Support Facility Dahlgren was established in 1918, in the final days of World War I, on 4,000 acres along the Potomac River in King George County, Va. At the time, it was a remote area, in a part of the river that’s wide and relatively straight, providing a clear shot all the way to the mouth of the Chesapeake Bay.

“This is the largest open water test range in the country,” say Dean Naujoks, with the Potomac Riverkeeper Network, one of the groups filing suit. “The Navy does not have a permit to discharge, and they’re discharging big weapons, projectiles. They’re doing experimental weapons testing.”

According to the lawsuit, filed by Potomac Riverkeeper and the Natural Resources Defense Council, the Navy is in violation of the Clean Water Act, because it does not have a permit to discharge pollution into the river. While the military can be exempted from the Clean Water Act by the president, the Navy does not have such an exemption at Dahlgren, according to the suit.

On a yearly basis at Dahlgren, the Navy fires 6,000 bullets, 4,700 projectiles, and detonates 190 explosives. It conducts tests using electromagnetic energy 490 times a year, lasers 60 times a year, and carries out chemical and biological defense tests 12 times a year.

In total the Navy has discharged more than 33 million pounds of munitions into the river, containing “toxic metals, solvents, explosives, and other potentially harmful constituents,” according to the lawsuit.

A Navy spokesperson said in an email to DCist that the Navy does not comment on ongoing litigation.

In an environmental impact statement released in 2013, the Navy argued that its weapons tests have negligible impact on water quality, habitat, and wildlife in the Potomac. According to the Navy, 98% of the projectiles are inert or duds, meaning they don’t explode, and rather sink into the soft river bottom, where they slowly and harmlessly disintegrate.

“Metals and explosives in buried ordnance would leach slowly into the surrounding subsurface sediments, with no direct contact to surface water or sediments,” the report states.

The 2% of projectiles that do explode, the Navy contends, scatter pollution so broadly that it is not a concern.

“After detonation of live projectiles above the water, small fragments or particles would be deposited on the surface of the water, which would then disperse over a wide area upon entering the water column. Limited amounts of material would be deposited in any single area, and constant water movement in the river would redistribute smaller particles after they settle on the bottom,” the report says.

The Navy contends the Potomac is a critical testing site that “replicates the littoral areas of the world where almost 45% of the world’s population lives and in which the Navy operates.”

The Navy’s testing on the Potomac impacts recreation and fishing on the river, according to the lawsuit — the weapons tests add up to a total of 750 hours a year, during which time use of the river by civilians is curtailed.

“You can certainly hear it,” says Mike Lightfoot, a waterman who catches rockfish in the Potomac and harvests oysters in a nearby tributary. “When they’re firing, you hear it, it sounds like a big thunderstorm.”

Lightfoot says he and other watermen support the lawsuit, and have concerns about what the Navy is putting into the river.

“We would just like to know what is on the bottom and what that means for the quality of water and the health of the Potomac River,” Lightfoot says.

The suit was filed in the U.S. District Court in Maryland — though the Navy facility is in Virginia, Maryland has jurisdiction over the Potomac River waters.