I lived in Queenstown a few years ago and did this. It's insane - the water really is ~6 inches deep in places and they get you unbelievably close to the walls. The boats all have huge scuff marks and dents where they 'missed'. In NZ, you can't really sue anyone. They have signs everywhere basically saying 'Know your boundaries cause if you get hurt, it's your bad'.
Awesome place. You should also check out videos for the Canyon Swing and the Luge. Crazy fun place.