Lakes in Wisconsinâs Northwoods average 148 days of ice-cover, so when the ice finally goes off in late April, the return of open water is greeted joyously! Thereâs an icing on this cake, too â common loons almost always return within 24 hours of the iceâs departure, having bided their time mostly on the open water of the Wisconsin River. People watch intently for the loons to arrive, hoping that âtheirâ loon pair will grace their lake for another year. Loon competition for prime lake real estate is so intense that a lake can be only partially open and the loons will land.