The U.S. Department of Transportation is warning people from interacting with certain shipwrecks. 

The notice, issued Monday in the most recent edition of the Federal Register, warns that U.S. custody and control extends to any wreck of a vessel that was owned or under charter of the Maritime Administration at the time of its sinking. Ownership titles are indefinite in most cases, and applies to all wrecks no matter when or where they sank. 

These wrecks are "highly threatened by illegal salvage," the notice said. 

The administration will allow for activities at a shipwreck, but permission in writing must be obtained, and the administration "prefers non-intrusive, in situ research," though it recognizes that "in certain situations disturbance or artifact recovery may be justified or become necessary." 

That control also covers shipwreck cargo, since it is covered by the administration's insurance programs and paid for by the same. War graves associated with Maritime Administration-protected wrecks are also protected, the notice said. 

"No disturbance or recovery from these shipwrecks or their cargoes may legally take place without the express permission of MARAD," the agency said. "Those engaging in unauthorized activities involving shipwrecks and cargoes ... are advised that no disturbance or recovery from said shipwrecks and their cargoes whether located in the waters of the United States, a foreign nation, or international waters." 

There are an estimated  20,000 shipwrecks in U.S. waters, according to the National Oceanic and Atmospheric Administration.

In:
• Shipwreck
• Oceans

Kerry Breen is a news editor and reporter for CBS News. Her reporting focuses on current events, breaking news and substance use.