WowAce

Recover the Cargo! in Dustwallow Marsh is I guess not covered. You use item Salvage Kit at the Shipwreck Debris to loot strongboxes, you are given a 'Repaired Diving Gear' to wear to do the quest, it does not appear to be in a subzone but general 'Dustwallow Marsh' out in the water, maybe key of wearing of the diving gear?

Edit: It also gives you the buff "Repaired Diving Gear"  if that's easier to track than items.