Time series of mean over-lake precipitation, evaporation, and river runoff (measured as the effect on lake level) for the 1950–2016 period for (a) Lake Superior, (b) Lakes Michigan/Huron, (c) Lake Erie, and (d) Lake Ontario. (e) Time series of net basin supplies (NBS) for the 1950–2016 period for Lakes Superior, Michigan/Huron, Erie, and Ontario. Red lines and text represent linear trends. *Significant trends (there is only a 5% possibility that such changes are due to chance). Lakes Michigan and Huron are connected by the Straits of Mackinac and thus have the same water level. They are therefore considered as one lake.