There was a strong maritime tradition with thousands of vessels that were lost along the Swedish coastline. There are between 9,000 and 10,000 registered and documented shipwrecks of both wooden and steel vessel types. Researchers estimate that there are a total of 40,000 known wreck positions in the Baltic Sea. Sweden is in the unique position of not having any woodworm to destroy the wrecks as well as low-salt levels and preservation qualities of the water in the Baltic Sea.

I find it fascinating that history has stood still from precisely the point in time the vessel went under. Additionally, if you are the first person to discover a wreck you can find many clues as to why the ship foundered and how people lived at that time.
 
Diving to an undisturbed wreck is like travelling back in a time machine. Permanent ancient underwater monuments might be, for example, dwelling places, fortifications, tollgates etc. Archaeological finds are objects that lack an owner, and are older than 100 years or have been found in permanent ancient monuments and are is some way connected.

Derelict could be an abandoned vessel without master or a find from such a vessel. The owner should not be traceable. Derelict could also mean objects found on a beach or that have been washed up onto a cliff. Jetsam refers to finds made on the seabed that are covered by water.

Flotsam are articles floating on the water not touching the seabed. This type of find should be reported to the police. The find becomes the property of the finder, unless the owner has reported the articles as missing within the prescribed time, usually three months.
 
Lagan refers to finds that can be traced to particular vessels by marking or suchlike. Lagan is reported to the police; the find is the property of the owner providing he wants it. The goods may also belong to the insurance company, and the insurance can be paid to the owner.