From the Iowa DNR 

Ice fishing shelters, left unattended, must be removed from state-owned lands and waters, including parking lots and boat ramps by Feb. 20. Ice fishing shelter owners who camp in their shelter can remain on state-owned land past the Feb. 20 deadline if they pay for a campsite in a state park campground. Ice fishing shelter owners are encouraged not to wait until the last minute to get their shelter off the ice. If a shelter falls through the ice, the owner is responsible for getting it out of the lake.