Lake Erie Water Levels 

Seasonal fluctuations range on average from 12 to 18 inches from winter lows to summer highs. The Great Lakes are generally at their lowest levels in the winter months. In the fall and early winter, when the air above the lakes is cold and dry and the lakes are relatively warm, evaporation is greatest. As the snow melts in the spring, runoff to the lakes increases.  Evaporation from the lakes is least in the spring and early summer when the air above the lakes is warm and moist and the lakes are cold. At times, condensation on the lake surface replaces evaporation. With more water entering the lakes than leaving, the water level rises.

Long-term fluctuations occur over periods of consecutive years and have varied dramatically since water levels have been recorded for the Great Lakes. Continuous wet and cold years will cause water levels to rise. Conversely, consecutive warm and dry years will cause water levels to decline. Long-term fluctuations are shown on the hydrograph under Tracking Water Levels below. A hydrograph is a plot of water levels versus time. Global warming and a phenomenon known as the ‘greenhouse effect’ could cause significant changes in long-term lake levels. Although debatable, most predictions indicate that global warming would cause prolonged declines in average lake levels into the future. Besides natural climatic variability and potential man-made climate change, other factors can affect long-term fluctuations, including changes in consumptive use, channel dredging or encroachment and movement of the earth’s crust.