Kind of puts the Skook to shame.

That type of feature is more common than we think, just not to that size!  As the tide comes in, it pushes on the outgoing river flow and creates the waves.  There was a cool kayak video put out a few years ago by Rusty Sage, Corran, and Steve Fisher about an expedition to one of those Tidal Bores in Brazil called Pororoca... heres a youtube clip from a surfing expedition I found, I couldn't find one for the kayak expedition, although there is a DVD for it ( http://www.trailpeak.com/index.jsp?cat=sea&con=article&val=3380*ev  )