There's a dispute about the massive treasure an exploration company found in a ship wreck (named 'Black Swan' for the moment, because they don't know its real name yet) at the bottom of the ocean. The company claimed its right on the treasure (estimated to $500 million US), but Spain declared that the treasure was theirs, saying that it was found in their waters. However, the ship is said to be an English one, so the treasure may well belong to England.

Personally, I don't really know what to say about that kind of situation... Who does this treasure belong to?

That's a very good question.

International waters is supposed to be fair game when considering "salvage rights" on a ship. Not sure if there is an international agency that recognizes a filing for such rights or if that is made with the nearest coastal nation or a citizen's own home nation. There are specific rules that supposedly govern the salvage process to avoid modern-day piracy (don't perk too much Delta, not the pirates of old).

Even if the valuables were from a national treasury or reserve, a nation would be hard pressed to enforce recovery. Common sense would seem to dictate that there would be legitimate claims for recovery on 'works of art' like paintings, sculptures, etcetera that had owner registration or were perhaps museum loans. The pictures wouldn't fare well in sea water, am guessing. Not sure if "crown jewels" would fall under historical or artistic license to be returned back to it's appropriate owners (at least without some kind of reward involved in paying some of the costs of recovery).

Not sure nations are even entitled to file "salvage" against whatever vessels/contents were owned by private individuals or firms, not to mention the sticky mess if it actually belonged to another nation-state. Maybe there is a statute of limitations on ownership loss in regards to this?