Aah.

I had an idea involving the flood trap, but I don't want to ruin any of your plans. :P

EDIT: Taking a look at the Wondermap, there's only one river and that's Serenity River, leading from Waterfall Cave to the ocean. Guess I'll have to use that for my idea instead of the Flood Trap in Waterfall Cave, it'll work out methinks. 

[IMG]http://www.serebii.net/dungeon2/dungeon/Map.png[/IMG]