Last month, in February, my husband was walking on a trail in the woods in Massachusetts, alongside a fresh-water lake. The temperatures had been fluctuating a lot over the winter, so some areas were solid ice, others had partial ice, and others had free-flowing water, with some swirling current. There were rocks interspersed in the water and along the sandy edges.
On a section of one edge of the water he saw a raised, ramp-like structure. It had a bumpy top with some jagged edges. It was open on the sides underneath the risen section. It looked like ice and matched the mottled gray colors of the icy area surrounding it.
He was unable to get close to it, so he couldn't see the exact markings or texture. He only got one picture of it, from about 25 feet away.
To give you a broader view of the water, I've added the second picture, which is the same lake from around the bend.
What is this, and how was it formed?
EDIT as of March 29, 2018: I don't know if it will be helpful, but I found a third picture. This too is of the same lake, but around a different bend from both the first and the second.