These tracks across the ice were an interesting feature. They seemed to have fractures running through them (you can just see them if you look closely in this photo). I’m guessing that the fractures allow liquid water to the surface of the ice and thus cause the difference in colour and texture from the rest of the ice.
Either that or it’s giant snails….
Canon 7D, Sigma 10-20mm, 1/125 at f9.