Riverboarding is a boardsport in which the participant lies prone on their board with fins on their feet for propulsion and steering.
This sport is also known as hydrospeed in Europe. Riverboarding in USA, white-water sledging in New Zealand. More popular in NZ than in the states.
Claimer: Someone that makes a claim that they have been there and done that, can do anything you can do better than you. I hate "claimers"