Besides perhaps more arrows, more health and more ammo, I could think of very few things that would improve this map, since it's fun to look, fun to play, and I have to imagine that making the ship sink at the end of the map would be impossible to achieve. Really, this is a pretty great map.
One small suggestion that I might make would be to add "no lifeguard on duty" signs to the walls on the side of the pool, if you could manage to get a texture like that.