Abandoned Ship, Route 108, Hoenn sea

The Abandoned Ship as it appeared in the Pokémon Advance anime
(source)

When the S. S. Cactus was too old to continue service, it was crashed into the rocks and partially sunken to serve as a habitat for pokémon, as is customarily done with those ships in Hoenn.

This ancient vessel has turned into the Abandoned Ship on Route 108 and is now filled with holes.
Being partially sunk, a deck of this ship is entirely underwater and both the HM move Dive and the Mossdeep Gym Badge are needed to get through it.