This is the marmot that gnawed my backpack open.
Just kidding! I don't know what this is. Probably marmot, but any chance it could be a beaver? I saw sign of beaver nearby:
http://www.inaturalist.org/observations/7264544
Possible beaver chew marks on willow tree branch hanging apx. 8" above water.
images are framegrabs from video. Four or five beavers emerged from beaver lodge near sunset. Diving image isn't great but you can clearly see the flat, horizontal tail.