Jumping in a few months late here, but if you're still interesting in paddling around Yellowstone and the Tetons, check out the Yellowstone.net forum for a wealth of YNP & GTNP knowledge, not to mention awesome photos and some really great folks  :)  

Here is a link to one of several threads on canoeing in Parkadise.     (You need to Login or Register
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Paddling the Snake in GTNP is on my "to-do" list next trip, if I can pry myself away from wildlife watching.   ;D