Snapclaw resides in a cave in the eastern end of the trench. The cave is airfilled, so you don't need waterbreathing to fight him, but it's no short swim so don't dally too much on the way - there's sharks in the trench, too.
He's classified elite, and with good reason. With just gear from questing, you should be ready with your cooldowns when you first take him on, as he can both take and dish out a fair beating. Of course, some classes (kiters, tanks and those with tanking pets) are likely to find him a cakewalk, as he has no real surprises up his sleeve - unless you're taken aback by poison or wanting to not to get caught in this.