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Restoring the Region's Environment: Taking a Balanced Approach

While water levels in the lake and river are primarily determined by natural factors such as precipitation and runoff, the regulation of water levels and flows has provided great benefits to those who live, work and recreate in the Lake Ontario St. Lawrence River (LOSLR) basin.

The proposed new and more balanced approach to flow management seeks to create more natural water levels in the lake and river while continuing to provide the basin community with substantial benefits. At the same time, some groups and communities would see some changes to the benefits they receive under the current plan.


The proposed plan is expected to significantly improve the health of Lake Ontario and the upper St. Lawrence River. In particular, it would improve the diversity and functioning of the coastal wetlands that cover 26,000 hectares (64,000 acres), filter runoff, reduce erosion and provide habitat for hundreds of fish and wildlife species. How can we measure this environmental improvement? A key indicator is the growth of a highly diverse plant community, known as wetland meadow marsh, following periods of low water supply. Under the proposed regulation plan, the portion of coastal wetlands with conditions that favor meadow marsh would be more than 40 percent greater on Lake Ontario and the upper St. Lawrence River than the area with favorable conditions under the current plan, restoring diveristy to thousands of hectares of wetlands.

There are several reasons why the wetland meadow marsh community is an excellent indicator of ecosystem health on Lake Ontario and the upper St. Lawrence River. First, wetland meadow marsh is ecologically significant in its own right and provides diverse habitat for many animal species. Second, it is sensitive to changes in the patterns of water level fluctuations caused by the regulation plan. Third, there is a high degree of certainty in the results. Field surveys and aerial photography show that the plant communities in coastal wetlands correlate strongly with the history of flooding and dewatering at specific locations. Finally, the indicator is broadly representative and generally consistent with results for other indicators, including shore birds, fish and other animals.

For the lower St. Lawrence River, modeling results do not show significant environmental changes under the proposed regulation plan. The difference between regulation plans is dampened by the variations in water levels caused by other factors such as inflows from the Ottawa River.

A table in the library summarizes the results for key environmental indicators on Lake Ontario, the upper St. Lawrence River and lower St. Lawrence River.

Costal Property

Under the proposed new approach, shoreline property owners on Lake Ontario would retain a water regulation plan that reduces the frequency and severity of high water levels on the lake, relative to unregulated levels. But because there will be greater fluctuations than under the current plan, there could be additional costs for some property owners, primarily through greater costs for maintaining and improving shoreline protection structures.

Property owners along the lower St. Lawrence River will see little change because the lower river already sees more fluctuations in water levels due to the variable flows of the Ottawa River and other rivers further downstream.

In circumstances of extreme high water levels, all possible relief will be provided to shoreline property owners upstream and downstream.

Recreational Boating

Recreational boaters could also see some changes due to the slightly more variable water levels from year to year under the proposed new approach.

Boaters on the lake and upper-river would see more gradual decline in water levels in the fall. At the same time, during low water years, there could be fewer recreational boating days.

Recreational boaters along the lower St. Lawrence River will see little change. This is because the lower river already sees more fluctuations in water levels due to the variable flows of the Ottawa River and other rivers further downstream.


Commercial navigation could see fewer delays in the Montreal-Lake Ontario section of the seaway. In some years, lower water levels on Lake Ontario could impact commercial navigation. Commercial navigation at the Port of Montreal and downstream would be largely unaffected by the proposed new approach. The more stable and predictable flows would be expected to provide economic benefits to the region's hydropower plants. In cases of extremely low water levels, the proposed new approach would provide relief to navigation and power interests.

  • Background

Learn more about the history of regulating water levels and flows on Lake Ontario

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Let us know your opinions and concerns about water levels and flows into the LOSLR system.

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