A lazy river ride or which there are three options: exit early to enter Tassie's Twisters (bring your tube with you to the queue), go right at the fork and travel under cylindrical fish tank (housing cichlids), or go left and travel under (or around for those tentative) a waterfall to view the Commerson's Dolphin exhibit.
Roa's rapids is much better! Also I find the water is colder here than it is in all the other attractions. Quite slow and squashed. 5/10