Water levels in the Great Lakes and St. Lawrence River have been a complicated and contentious issue ever since the creation of the St. Lawrence Seaway which officially opened in 1959. Before then, water levels were determined by nature and the seasonal cycles of rain and evaporation.
Water from all five Great Lakes flows into Lake Ontario and eventually out to sea through the St. Lawrence River. It was only with the Seaway dams built to improve navigation through the St. Lawrence that water levels became a serious public policy issue because, for the first time, water levels could be mechanically manipulated. The earliest plan to artificially regulate and control water levels was implemented in 1958.
Since then, conflicting interests have competed and sometimes quarreled over too low or too high water levels. Commercial navigation - shipping - wants high levels to maximize the number of days ships can pass throughout the St. Lawrence River. Hydro electric power producers prefer a constant level in order to most efficiently produce electricity. Fishermen and marina owners generally like high water levels, lake front property owners want low levels so as to protect their shorefront property from erosion and damage, and environmentalists are concerned about either too high, or too low levels that endanger wildlife and the natural habitat that is the breeding ground for flora and fauna.