Environment

Century-Old Wetlands Spring Back To Life In Toronto’s Revitalized Waterfront

Scientists restoring Toronto’s Don River uncovered century-old soil, reviving native plants and offering new hope for successful wetland rehabilitation.

100-Year-Old Ecosystem Discovered Beneath Toronto

When crews began digging deep into Toronto’s industrial waterfront to restore the mouth of the Don River, no one expected the soil itself to fight its way back to life.

But buried beneath more than 20 feet of fill dirt, untouched for more than a century, ecosystems lay in wait.

Quick History Lesson

The area, now part of the Toronto waterfront's Biidaasige Park, was once one of the largest peat wetlands in the region. In the early 1900s, it was filled in during industrial expansion, forcing the adjacent Don River into a rigid, engineered channel that worsened flooding and erased critical habitat.

Now, as part of a massive flood-protection and revitalization effort, construction crews excavating the new river valley noticed something unusual.

“That was exposing soils that hadn't seen the light of day in over a hundred years” said Dr. Melanie Sifton, a postdoctoral fellow in forestry and conservation at the University of Toronto. “Some plants started to germinate in the area that people didn't quite expect."

Newly exposed soils in the excavated river revealed unexpected plant growth, as dormant native species re-emerged after more than a century underground.
(Dr. Melanie Sifton/University of Toronto)

Scientists, engineers, architects and Indigenous community members quickly realized what was happening: Native wetland plants, buried since before the industrial era, were sprouting on their own.

A Living Time Capsule

Sifton helped carefully extract dozens of soil samples (what she affectionately calls “soil cookies”) and took them back to University of Toronto greenhouses.

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What followed was even more astonishing.

Researchers identified pollen records that revealed which plants once dominated the landscape before industrialization.

Seeds from rare species emerged, including butternut, now endangered in the region, along with fast-growing willows and wetland shrubs.

“Even without active intervention by us humans, by just uncovering these soils, they were starting to come alive and still held life on their own without us even having to do anything," Sifton said. "They were just coming back alive after being unburied.”

As the samples were studied more closely, it became clear the revival wasn’t limited to vegetation.

Early signs of ecological recovery appeared as wetland vegetation began to establish across the freshly uncovered channel beds.
(Dr. Melanie Sifton/University of Toronto)

“Soil is alive,” Sifton said. “We started to notice other kinds of creatures. Even I started to notice different kinds of insects.”

Under microscopes, researchers began spotting bacteria and tiny organisms, evidence that entire components of the ecosystem may have endured in dormancy.

Lessons Beneath Our Feet

Wetland restoration often struggles, largely because it’s difficult to recreate the complex systems that make them function.

“We can never go back to exactly what was before," Sifton said. "We can look at the history and learn from that and then potentially work with what was there to learn what might be possible again.”

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What made this project different was its willingness to listen to the land.

“The soils sort of spoke to us very quickly,” she said. “They showed themselves to be full of life vibrancy and ready to go.”

With water restored to the river, former construction pathways transformed into active waterways shaped by revived soils and returning plant life.
(Dr. Melanie Sifton/University of Toronto)

Rather than replacing contaminated soils with new material, engineers cleaned and reused much of what was already there, preserving the ecological memory embedded underground.

“Using what was already there as a foundation to rebuild was really important,” Sifton said.

The benefits extend far beyond scientific discovery. Flood risks in downtown Toronto have already been reduced, even during major rain events. Wildlife is returning. Fish species unseen for a century are reappearing. Birds, mammals and insects are reclaiming space once lost to concrete.

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“Wetlands are the lungs of our region,” Sifton said. “We really need to appreciate them and support them, not fill them in.”

For Sifton, the project also carries a deep message about evolution — one that reaches below the surface.

“We see the trees, we see beautiful plants and flowers and what's happening above ground, but that there's a whole life under the ground that we need to also be paying attention to and to support," she explained. "There's a lot of valuable lessons that we can learn from what's going on under the ground and the history in the soil."

Understanding and respecting that hidden world, she believes, could transform how cities approach restoration and resilience.

“That’s my dream as a plant and soil scientist,” Sifton said. “That we think more and respect the soil more in the future.”

weather.com lead editor Jenn Jordan explores how weather and climate weave through our daily lives, shape our routines and leave lasting impacts on our communities.