Several beaches along the Delaware, Maryland and Virginia coastlines are closed to swimmers after medical waste washed ashore.

All ocean-facing beaches on the Assateague Island National Seashore, a 37-mile-long island along the coasts of Virginia and Maryland, are closed to swimming or wading, the park office announced in a Facebook post on Sunday. The seashore is part of the National Park Service and is open year-round.

"We currently have no idea where it came from and will not be speculating about a source," the park office said in a post. "Health authorities will be investigating."

Closures extended north into Delaware, where officials in Dewey Beach and Fenwick Island announced they were closing their beaches to swimmers on Sunday.

"The source of the medical waste is still under investigation, and DNREC continues to monitor the situation closely," Delaware Department of Natural Resources and Environmental Control spokesperson Michael Globetti told the Delaware News Journal, part of the USA TODAY Network.

The agency advises beachgoers to "leave the beach and refrain from swimming in the ocean," he said. The agency also encouraged beach visitors to wear shoes.

Few details about medical waste

The Assateague Island National Seashore said the waste started to come ashore Sunday morning. Those who were in the water earlier days "should have nothing to worry about," the agency said.

The park service has "no idea" where the medical waste came from, but said health authorities are investigating.

The park service added it did not know how long closures would be in effect.

Assateague Island National Seashore closures

According to the Assateague Island National Seashore office, the closures include:

◾ All of the island north of Assateague State Park is closed to all visitor access.

◾ Assateague Island State Park Beach is closed to swimming and wading.

◾ All oceanside beaches in Assateague Island national park are closed to swimming and wading, including North Beach, Oceanside Camping Beach, South Beach, the beach on the Over-sand Vehicle Area and the Chincoteague Beach.

Officials in Delaware also closed beaches in Dewey Beach and Fenwick Island.

Shannon Marvel McNaught reports for The Journal News, Keith Demko reports for the Salisbury Daily Times and Gabe Hauari reports for USA TODAY.

Shannon Marvel McNaught reports on southern Delaware and beyond. Reach her at [email protected] or on Twitter @MarvelMcNaught.

Gabe Hauari is a national trending news reporter at USA TODAY. You can follow him on X @GabeHauari or email him at [email protected].