The Quiet Disappearance of Coastal Wetlands in Ontario
Stand at the edge of Long Point on Lake Erie and look inland, and you are seeing one of the largest remaining coastal wetland complexes in the Great Lakes basin. Thousands of hectares of marsh, swamp, and shallow open water stretch behind the sandy spit, filtering nutrients, sheltering migratory birds, and absorbing floodwaters before they reach surrounding farmland. Long Point is a UNESCO World Biosphere Reserve, a globally significant ecological site. It is also increasingly an outlier.
Across southern Ontario, coastal wetlands have been disappearing for more than a century. The losses have been gradual enough that most people never noticed. A marsh gets filled in to expand a marina. A swamp gets drained to make room for a subdivision. A shoreline cattail stand gets cleared so a property owner can see the lake. Individually, each loss seems small. Collectively, they represent one of the most consequential environmental changes in Ontario's history.
How Much Has Been Lost
The numbers are sobering. Southern Ontario has lost an estimated 72 percent of its pre-settlement wetlands, according to data from the Ontario Ministry of Natural Resources and Forestry. Along the Great Lakes coast specifically, the losses are even steeper. In some watersheds draining into Lake Ontario and Lake Erie, more than 85 percent of original coastal wetlands have been converted to agricultural land, urban development, or industrial use.
The pace of loss has slowed since Ontario introduced provincial wetland protection policies in the 1990s, but it has not stopped. Between 2011 and 2021, satellite monitoring by the Ontario Ministry of Natural Resources and Forestry documented continued encroachment on evaluated wetlands, particularly along the Lake Simcoe and Georgian Bay shorelines where development pressure is intense.
Why Coastal Wetlands Matter More Than People Think
Wetlands are often described as the kidneys of the landscape, and the analogy holds up well. A single hectare of healthy coastal marsh can remove kilograms of phosphorus and nitrogen from water flowing through it before that water reaches the lake. These are the same nutrients that, in excess, fuel toxic algae blooms. Lake Erie's recurring bloom problem is directly linked to the loss of wetlands that once filtered agricultural runoff before it entered the lake. For more on that connection, read our report on algae blooms and the future of Lake Erie.
Wetlands also function as natural sponges during high-water events. They absorb and slowly release flood waters, reducing peak flows in downstream creeks and rivers. Communities that have lost their upstream wetlands tend to experience more severe flooding, more often. The insurance industry has started paying attention. A 2020 study by the Intact Centre on Climate Adaptation estimated that restoring just ten percent of lost wetlands in some Ontario watersheds could reduce flood damages by hundreds of millions of dollars.
Then there is biodiversity. Coastal wetlands are among the most productive ecosystems in the temperate world, supporting more species per square metre than almost any other habitat type in Ontario. They are critical breeding grounds for northern pike, largemouth bass, and dozens of forage fish species. They provide nesting habitat for species at risk, including the least bittern, the Blanding's turtle, and the king rail. When a wetland vanishes, its ecological output does not simply relocate. It disappears.
What Is Still Driving the Decline
Despite stronger regulations, several forces continue to degrade Ontario's remaining coastal wetlands. Fluctuating lake levels, amplified by climate change, can drown out marsh vegetation during high-water periods and allow invasive species to colonize during low-water years. Phragmites australis, an aggressive non-native reed, has taken over vast stretches of Great Lakes wetland, forming dense monocultures that crowd out native plants and reduce habitat value. We cover this threat in detail in our article on invasive species changing Ontario waterways.
Nutrient loading remains a persistent problem. Runoff from surrounding agricultural land and urban areas pours phosphorus into coastal wetlands, triggering excessive algae growth that smothers aquatic plants and depletes oxygen. Some wetlands that appear healthy from the surface have already lost much of their ecological function beneath the waterline.
Development pressure has not gone away either. Ontario's population is projected to reach 20 million by 2046, and much of that growth is concentrated in the Greater Golden Horseshoe region along the Lake Ontario shoreline. Every new subdivision, highway extension, and commercial development adds impervious surface area that increases stormwater runoff and reduces the buffer between developed land and remaining wetlands. Our piece on stormwater runoff in waterfront towns explains the mechanics of this process.
Protection Efforts and Their Limits
Ontario's wetland evaluation system, which classifies wetlands as provincially significant or locally significant based on biological, hydrological, and social criteria, has been the backbone of wetland protection since the 1980s. Provincially Significant Wetlands receive the strongest regulatory protection under the Provincial Policy Statement, which generally prohibits development within and adjacent to them.
But the system has gaps. Locally significant wetlands receive weaker protections and can be more easily lost to development approvals. Small, unevaluated wetlands, many of which provide important ecological functions, fall outside the formal classification system entirely. And enforcement of existing protections has been uneven, varying significantly from one municipality to the next.
Conservation authorities have stepped into some of these gaps, using their regulatory authority under the Conservation Authorities Act to protect wetland areas within their jurisdictions. The role they play, and the tools they have available, is explored in our article on how conservation authorities regulate shoreline activity.
Restoration: Possible but Difficult
Restoring a coastal wetland is not as simple as reflooding a drained field. The hydrology has to be right, which often means reconnecting the site to its original water source and removing decades of accumulated fill. Native plant communities need to be reestablished, and invasive species have to be managed continuously, sometimes for years, before the restored wetland can function on its own.
The costs are substantial. A large-scale wetland restoration can run from $50,000 to $200,000 per hectare depending on the site conditions and level of degradation. But the return on investment, measured in flood reduction, water quality improvement, and carbon sequestration, consistently exceeds the cost. A growing body of research from the University of Guelph has demonstrated that restored wetlands can recover 60 to 80 percent of their original ecological function within a decade if the work is done properly.
Several ambitious restoration projects are now underway across the province. Ducks Unlimited Canada, in partnership with conservation authorities and First Nations communities, has been leading efforts to restore degraded wetlands along the Lake St. Clair shoreline, one of the most heavily impacted areas in southern Ontario. These projects represent some of the most encouraging conservation work happening in the Great Lakes basin today.
The quiet disappearance of Ontario's coastal wetlands has been one of the province's most consequential environmental stories, unfolding over decades without the drama of an oil spill or a factory closure. Reversing the trend will require sustained investment, stronger policy, and a broader public understanding that these soggy, often unremarkable-looking landscapes are doing more for our communities than almost anyone gives them credit for.
