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Indiana Department of Natural Resources

Water > Lake Michigan > Regulation of Great Lakes Lake Levels Regulation of Great Lakes Lake Levels

Presently the International Joint Commission implements plans under which limited regulation of Lake Superior and Lake Ontario takes place. The regulation of Lake Superior influences the whole Great Lakes System, however, regulation of Lake Ontario has no impact on the upper lakes because of the difference in elevation at Niagara Falls which acts as a control. The outflows of Lake Superior and Lake Ontario are controlled to keep the lake levels within a specific range, near their long-term averages. Levels of Lake Superior have been regulated since 1921. Levels of Lake Ontario have been regulated since 1958. In addition, five Great Lakes diversions also contribute to regulation of lake levels.

Current regulations of lake levels do not affect long-term lake level trends and cannot influence lake levels significantly in the short term. Regulation can only partially alter or alleviate lake level extremes. However, suggestions to alleviate problems caused by high water levels included altering the regulation plans for the Great Lakes. Generally, regulatory changes require approval by the International Joint Commission.

Changes in water levels of the Great Lakes from diversions and control works require a significant amount of time to take effect due to the amount of surface area of this lake system. On the upper lakes, it takes approximately three and one half years for one-half of the anticipated result to occur. The full effect of change could take between twelve and fifteen years.

The regulation plan of Lake Ontario outflows is administered by the International St. Lawrence River Board of Control. The plan was instituted in 1963 to accomplish several goals including the:

  1. provision of deep-draft navigation through the St. Lawrence, Lake Ontario system;
  2. provision of hydroelectric power generation,
  3. protection of shoreline property owners; and
  4. improvement of Montreal Harbor levels.

The outlet of Lake Ontario is regulated by a series of structures and channel enlargements. The Iroquois Dam, Moses-Saunders Power Dam, Long Sault Dam and the Eisenhower and Snell Navigation Locks contribute to the control of lake levels. The main control structure, Moses- Saunders Powers Dam, has the capacity to discharge 333,000 cfs of water from Lake Ontario in the St. Lawrence River. The long-term average outflow of Lake Ontario is about 240,000 cfs.

The regulation plan of Lake Superior outflows is administered by the International Lake Superior Board of Control. Varying the amount of water allocated to hydropower production in conjunction with adjustments of the gates in the Compensating Works at the head of the St. Mary's Rapids, the outflow from Lake Superior to Lake Michigan - Huron is regulated. From May 1 to December 1 the gates of the control works are set monthly. The outflow is a function of the mean Lake Superior level and other factors form the prior months as well as forecasts of future outflows. This flow can vary from 55,000 to 134,000 cfs. The plan requires that Lake Superior not be allowed to rise above 602 feet above sea level, under normal conditions.