I think it could be a net or something similar indeed. What I find suspicious about this video is that, whether deliberately or not, but the camera avoids to show us the 'head' of the supposed 'creature' or it's alleged 'movement' against the water flow - to make such conclusion we need to watch the shore simultaneously which we can't in this case. Otherwise this 'thing' could be simply attached to something else (a boat?) with a rope and just be floating in the water without actually moving forward.
Just some thoughts, it could be a creature too, who knows. FWIW