Guideboatguy is right on. I think of a bicycle helmet like a car airbag -- you hope never to need it, and once you use it, it's done. Paddling helmets, on the other hand, are designed to stand up to multiple impacts, and particularly if you're paddling whitewater, chances are you're going to need it more than once. My helmet has certainly saved my noggin on several occasions.
Another difference is that most bike helmets have vents/holes in order to allow air to circulate over your head while riding. That's fine for their intended purpose, but definitely NOT a feature I'd want on the river.
Kayak & Canoe Covers
Canoe / Kayak Anchors
Classic Freestanding Rack
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