Juro it is;
Ice with sand on top of it.
All the ice in Lake Michigan comes down to the Southern end and piles up. Meanwhile the waves and wind blow sand on top of it.
I have some old photos from the 80's where ice was as tall as a 2 story house.
Nice thing about winters like that is that our warm water discharges (power plants mills etc) draw fish like a magnet. Bad part is it is very very ugly. But if one must capture a fish in sub zero weather it does the trick.