Why Water Levels Fluctuate
Even with the hydropower dam, water levels on the lake and river are determined largely by natural factors such as precipitation, evaporation and runoff.
Unregulated and uncontrolled flows into the lake and river abound. For example, an average of 80 percent of the water flowing into Lake Ontario comes from Lake Erie over Niagara Falls and uncontrolled water from the Ottawa River has a major influence on water levels in the Montreal area and downstream.
The only significant factor that can be regulated is the outflow from Lake Ontario at the Moses-Saunders Dam. The outflows from the dam can have a rapid effect on water levels in the St. Lawrence River upstream and downstream of the dam, but have a more gradual effect on Lake Ontario water levels.