And the biggest problem with those situations is that you often have no idea where they are until all of a sudden you are stuck.
Had it happen to us once with a quad on a remote lake 20+ kms from the truck. Was driving along and all of a sudden water is flying up around us and the quad was sinking... I thought we had broke through for some reason but fortunately it was only a foot or so of water on top of the ice. We had to unhook the sled and push the quad out, if we had been using a truck we would have been stuck for good.
Pictures I saw from Utikuma and Swan Hills area looked similar and were both from this weekend.
I would definitely be sticking to the main trails if going out fishing right now. You never know when you will hit something like this or a snow covered crack/ridge etc.