Is it a live mammoth? Is it a bear in some odd activity that makes it look that way?
How about it's a complete hoax? The fact that the focus is crappy and stays crappy is something of a giveaway. Looks to me like some footage of an elephant slapped together with some footage of a river. Unprofessionally.
There are some arguments for it being a grizzly bear with a fish hanging out of its mouth. That's not entirely out of the question, but still puts us in hoax territory, as it's surely shown out of focus on purpose.
Try harder next time, guys.