I was curious when a saw a few of these piles of vegetation heaped up above the water's surface in a shallow cove, so took a few pics and looked it up for matches on Google lens.
I believe these untidy looking collections of vegetation are from muskrats' activity - they're preparing winter dens from which they can gnaw through the ice and have access to their watery larder - ice fishing, with their very own shelter.
It does look pretty untidy, but when you look up close, it almost has some artistry and skill!
This neater one is quite picturesque!