Winter ice helps to protect lake water from evaporation and keep water levels high. In recent years ice hasn't been as plentiful: http://thinkprogress.org/clima

Winter ice helps to protect lake water from evaporation and keep water levels high. In recent years ice hasn't been as plentiful: http://thinkprogress.org/climate/2012/03/31/455612/great-lakes-ice-cover-down-71-since-1973/ http://thinkprogress.org/climate/2012/03/31/455612/great-lak... Keep in mind that 2012 was an very, very warm winter even compared to the years leading up to it.