most electric forklifts are a little low on low horsepower to be viable EV donors. your going to need something in the 60-70hp rating range to get any kind of stock-ish performance out of an EV.
as far as water crossings, i dont think the motor would be much effected by fresh water (mud may be a problem, but filters could probably be implimented). the batteries couldnt care less if they get wet. the controller would have to stay dry...but it can be mounted pretty much anywhere on the vehicle.