As it turns out, some evidence has (finally) emerged which seems to show higher waterfalls being run by hydrospeed / riverboard, than the one shown in the image above.
Read the full article here > http://facelevel.com/2012/12/riverboarding-15m-hollin-chico-waterfall-in-ecuador/
Nonetheless, this waterfall descent by Josh Galt remains probably the biggest waterfall run by hydrospeed / riverboard for the last 2 decades. For more, visit http://www.joshgalt.com and http://www.facelevel.com
The future is looking exciting for the sport!