Last time I was there was about 3-4 years ago. The course was situated in the 'lagoon' on the opposite side of the road where all the hotels/resorts were located. I never saw anyone ski on it but I did notice it wasn't in the best condition (i.e. - buoys missing, out of alignment, etc.). Since I never saw anyone ski on it, I have no idea what boats they used to pull a skier. I'm pretty sure the water is at least brackish if not salt water.
As an aside, we ate at a restaurant on the shore parallel to the course and one of their draws was the ability to feed the gators from the deck just after dark. There were enough to cause me to wonder whether I wanted to spend lot of time swimming in that water!! :)