"muddy unknown"? What the heck?
Also, note the "muddy grass" and whatnot around the southern and western edges of the pool.
The "Unknown" squares were normal ice, before the spring thaw. When the thaw hit, the pond -overflowed-, creating the muddy stuff around the edges. The "unknown" squares were also created. I imagine the water that -should- have been there, is what overflowed.
I still don't know what's going on.