The dangers are that the fish suck up all the oxygen. that can take very little time to be deleted in an over stocked pond. The cold isn't realy an issue unless your pond is very very shallow. But even then in your area i doubt the ice will get thicker then a couple inches if even that. If you can drill a hole through the ice or even use a sawsall being VERY careful not to penetrate to far beyond the ice and only cutting in a deeper area. placing a air stone in there to help replenish the 02 and it will also let out co2