The Detroit News Alder Falls runs into Lake Superior's Big Bay.
Small streams are important suppliers to all the lakes.
Rain and snow needed to replenish the system have dropped by as much as 25 percent over Lakes Superior, Huron, Michigan, Erie and Ontario during the past 18 months. Warmer winter temperatures also are preventing protective ice sheets from forming, leading to greater evaporation. In a loss usually noted in summer months, inches of water can slip away under the heat of the sun's rays in a matter of two or three days. Water escapes as vapor and is quickly carried by winds into the atmosphere. As many as eight inches can evaporate in a single month.