Artifact regulations and laws are all over the place.
In the US they range from The Great Lakes where in State Waters, anything over 50 years old is considered to be State property, NY has the same regulations. Then across Long Island Sound CT has no specific wreck regulations but does say that anything embedded in State Lands, is State Property. The bottom of all of the Great Lakes under US control and all of Long Island Sound is considered to be State Lands.
Seaward, State lands are either 3 miles for most of the US with the exception of the Gulf of Mexico where it is 9 miles.
So, startting at the Low Water Line:
State Waters: 0-3 or 9 as above
Federal Territorial Waters: from State Waters out to 12 Miles
Federal Continuous Zone: 12 miles to 24 miles
Exclusive Economic Zone: 24 miles to 200 miles
The US has no laws on wreck preservation beyond State Waters. Even within State waters if you can show ownership of a wreck, say by buying the rights of the wreck from an insurance company, then State waters are void see the Brother Jonathan Case.
Outside of 200 miles are international waters and is an open game
Strict reading of the UN Law of the Sea has wrecks from 12 miles out as unprotected but some countries use 24 or even 200 miles. Within these zones the laws range from what Greece used to have which was no scuba anywhere unless specifically allowed, which was usually in resort areas only, to the US where you can dive just about anywhere outside of a specifically secure area. There is a new UN UNESCO treaty that is inforce for those countries that have signed it that tries to protect all wrecks no matter where located. The countries that have signed the treaty are:
Albania
Barbados
Bosnia and Herzegovina
Bulgaria
Cambodia
Croatia
Cuba
Ecuador
Gabon
Grenada
Haiti
Iran
Italy
Jordan
Lebanon
Libyan
Lithuania
Mexico
Montenegro
Nigeria
Panama
Paraguay
Portugal
Romania
Saint Kitts and Nevis
Saint Lucia
Slovenia
Spain
Tunisia
Ukraine
You will notice that the major modern maritime nations have not signed, and most likely will not sign, it.
It also really helps when the wrecks in question are in an area where long term preservation is possible. In the Great Lakes and the Baltic the fresh water preserves the wrecks just about indefinably by human terms. So a wreck 100-200-500+ years old is seen as a wreck. In Truk, the coral growth and location in a protected lagoon protects the steel wrecks. But, off the Atlantic Coast, there is not growth protection like in Truk, the wrecks get broken up quickly by storms, many were wire dragged if shallower then 100feet, and almost from before the 1960s have seen some commercial salvage at the time of sinking. In other words, Atlantic wrecks look a lot more like junk piles then a Hollywood wreck.
Last, the actual real protection of a wreck site has a direct relationship to the locals attitude to the wrecks. In many cases, Truk included, it was a fairly free recover zone until the locals found that an artifact on the bottom could be sold only once to a collector, or every day of the year to a divers with a camera. The artifacts are just worth more to the locals on the bottom then on a mantel piece. The same thing happened in the Great Lakes with the addition of the Zebra mussels. Before the Zebras, you just couldnt see a thing and hardly anyone went there, so to get divers recovery was allowed. Then after the Zebras the water cleared, you could see things, divers started coming, wrecks with artifacts on them increased in value, and they were protected.