When it reguarly gets very cold in the northern part of the state, they should have entertained the possibility of that happening. 500 k is a lot of money. 100 years ago is not that long ago.
OK a better way to have said it is that it doesn't usually get that cold for that long to warrant the heating system. It wasn't a 1 or 2 day affair. Water temps don't drop far enough to freeze overnight from the mid 70s.
Maybe you could also explain how you heat multiple ponds on 10 acres of land? I'm sure insurance against losing fish due to cold is much cheaper and more efficient.