Frozen, cannot build this palisade
I chipped out the ice, can now build the pali on the same tile.
This matters because it can prevent palisade repairs, it was discovered last winter by a friend, a new player trying to repair an old base and didn't understand why they could not repair the pali. It is still possible to do so if you dig out the ice, but it's not intuitive for swamps to only be considered "water" in winter.