there are no waves - the water level will depend on the time of year, but it is never really deep. You sit in an innertube and float slowly downstream, part of the way is through caves. In a couple of places the water was really shallow and we had to carry our tubes. The water was cool and refreshing after the hike through the jungle. It's a pretty easy trip and very worthwhile. I don't think there was any place more than about 4 ft deep and there are no rapids, the water moves prettly slowly. I highly recommend the trip!
Deacon, you should check it out when you make your first trip to SP this year - it's really not lots of water!