Is it possible to.....REALLY important please read....
 

ok well.... i got this really inovative idea but.... one little down fall is fans are not ment to work submerged in water.... hehe ill explain later when i get to crunching on this project...

anyways i was wondering if it is possible to make the fan work underwater like a normal fan.... what would it take to do so? coat the pcb with dow conformal coating? or what? it needs to spin and run like a normal fan.....

Yep, it´s called "propellers".
Don´t know if a standard fan can be modded. Sounds like shortcircuits to me.
http://www.mercurymarine.com/mercury_2.5_classic
Might be some noise and foul smell, but definetely a propeller.
OK, sorry, that one was a bit rude.
Haven´t heard about underwater propellers. Can´t a standard submersed pump do the trick? Don´t connect the hoses, and it will create a waterflow.
regards
Mikael S.

Hmmm..
Has this one spawned a new thraed?
eXtenz: No offense ment in my unserious reply. I do think You need to get the fan motor out of the water, so I thought for a while over a small electric motor outside the water, some connecting rod and a propeller, but MadDogMe had a better answer.
regards
Mikael S.