Lake Superior, the largest of the Great Lakes, might be smaller today if it weren’t for the Compensating Works, a 16-gate structure completed in 1921 that regulates the release of water from Superior.

The works are operated by the International Lake Superior Board of Control, established in 1914 by the International Joint Commission. David Fay, the Canadian member of the Board of Control, explains that the works were built to allow for hydropower development on the St. Marys River.

Water from Lake Superior flows through a collection of structures that stretch across the river, including three hydropower plants, five navigation locks and the works --- a gated dam at the head of the St. Marys Rapids.

The works got their name for the job they do: Helping compensate for river water that’s used for hydropower generation.

“It’s called the Compensating Works because it compensates for the additional flow that the hydropower plants take,” Fay said.

“If you think back to the late 1800s, all the water flowed over the (St. Marys) Rapids. There were no structures, it was free flowing. Then, hydropower plants were built and canals took additional water from Lake Superior, and more water was flowing out than would have occurred naturally.”

The Compensating Works control the flow of water at the Rapids, and allow the plants to keep operating, while helping to keep Lake Superior levels in check.

“If there had been no Compensating Works, it would have basically drained Lake Superior, to a point, and that would have affected navigation and people living around the lake and the environment,” Fay said.

The hydropower plants on the St. Marys today are parallel to the Compensating Works. Typically, only one to four of the 16, 50-foot-wide gates of the works remain partially open.

“It’s only when hydropower plants can’t discharge all the water that we require to be discharged that we start opening more gates,” he said.

The flow of water through the works is overseen by the International Lake Superior Board of Control. The flow is set monthly to accommodate hydropower generation and ship navigation, and maintain municipal and industrial water supplies and fish habitat.

“There is a regulation plan with a number of rules in it that looks at the balance of water levels on Lake Superior and Lakes Michigan and Huron and tries to keep them in relative balance compared to the average,” Fay said.

The Compensating Works only provide a small measure of control of lake levels. Factors like precipitation, evaporation and runoff have a much greater impact. As it is, only about seven percent of the lake’s flow passes through the Compensating Works.