I saw this in an icy lake earlier this week. It's not ice that has broken and then frozen over again, breaks in ice don't branch out like that. It's something else that happens to the ice due to something in the lake, but what?
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Looks like an impact pattern. Could be pressure too I spose, but that would probably take a lot of pressure quickly (hence my impact guess). That is an odd bit of branching, even for an impact. Looks like a fractal.