I road the seven spring wash and the horseshoe dam last year.
The seven spring wash was at the end of my circle loop, cruising just having fun. Totally wiped out on that slippery SOB, sent the bike scooting the whole way. I told the rangers, but I dont think they did anything.
BTW the best time to ride the walkway is when they are releasing the water - too cool. Even better is when they release it while you are under there. The world is coming down...