Buried treasure maps can only be found in shipwrecks and ocean ruins.

A sunken ship is an underwater structure similar to a sunken ship. Some shipwrecks may harbor creatures such as drowned bodies, so it's best to be cautious when exploring. In addition, shipwrecks can occur in a variety of different locations. In the image above, for example, you can see the side of the wreck stuck in the ice. They can also partially spawn on land or be buried on beaches.

Inside each wreck, you can find up to three chests containing various trophies. To get the treasure map, you need to find the map box. They're not marked, but this box will be located under the ship. If there is a map chest, there is a 100% chance that it contains a buried treasure map.

Similar to shipwrecks, you can find Marine remains underwater. They are fewer than shipwrecks and can be very dangerous to sail in. These structures were found in a Marine biome that looks like an underwater village. There will be crates full of loot in the buildings of ocean Ruins. You have a 43% chance of finding a buried treasure map in one of these boxes.

In general, searching for buried treasure maps in sunken ships is a better option.