Read the book Shadow Divers to get an idea how treacherous a wreck can be.

At least these guys don't have to worry about nitrogen narcosis, decompression, and coming up out of sight of the boat in the middle of the ocean if you lose the anchor cable... but they still have to deal with low vizibility, entanglement and disorientation.

Another one that gives me the chills is the story of the escape from the sunken sub S-5.