http://www.mostlytoasty.net/2011/06/22/surfing-standing-waves-waimea-river/

Standing waves are a cool phenomenon.  Growing up I got to play in some while whitewater rafting and then I encountered artificial, man-made  waves that were designed to let surfers stay in practice away from the beach (see very bottom video).  I thought that they looked like pretty cool toys, but failed to come close to simulating the complete surfing experience (disclaimer:  I am a horrible surfer).

Today I came across a semi-natural standing wave that looks a lot cooler than anything man-made.  The wave is created by diverting water from the Waimea River, which runs from the Alaka’i Swamp in Hawaii (the largest high-elevation swamp in the world)  to the Pacific.  Local surfers dig a channel from the river across the beach.  At fist this man-made channel carries no more than a small stream, but as sand is carried away by the water it becomes a raging torrent that produces a magnificent set of standing waves.

pretty awesome