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"It really is a rebirth," said Mayor Olivia Chow at a ceremony Friday in the Port Lands marking the final connection of the Don to the lake. "We now have new fish species coming back, wildlife, indigenous plants coming back."

Chow was among almost 100 attendees — some of whom arrived by boat — who stood in the crisp fall air at the newly built mouth of the Don.

"Today we're standing on the shoulders of so many people," said local Coun. Paula Fletcher, referring to the advocates for the river's regeneration in the 1980s, some of whom were at Friday's ceremony. "If they hadn't cleaned the river up, we would really not want it to be flowing out to the harbour, would we?"

"I'd also like to recognize the humility of making a river," said Laura Solano, partner at Michael Van Valkenburgh Associates, the firm that designed the Don's new river valley. “It's impossible to truly make nature from scratch. We can only dedicate ourselves to making the circumstances for nature to take hold."

The Don of time

Formed thousands of years ago by an ice age, the Don River is a 38-kilometre watercourse flowing from the Oak Ridges Moraine near Richmond Hill emptying into Lake Ontario through the Keating Channel in ɫɫ��'s eastern waterfront.

It's one of the most urbanized watersheds in Canada, covering a large swath of central ɫɫ��, North and East York, Scarborough and York Region. That intense urbanization means roads, homes and paved surfaces cover soil and vegetation, leaving fewer permeable areas to absorb water. Instead, when it rains, stormwater runs off and finds its way into the Don River, often resulting in floods.

Decline of the Don

All of this meant the Don was strong-armed into flowing only into the Keating Channel in an unnatural 90-degree turn, increasing the risk of flooding in the area, as there was significantly less room for it to flow into the harbour.

Over the years, due to the tank farm now lining the shores, the soil became so severely contaminated and the river so polluted from industrial activity that a group of university professors and students hosted a funeral in 1969, marking the Don's decay.

A trickle becomes a flood

Friday's successful regeneration of the Don's mouth started with a group of volunteer advocates in 1989.

An event at the Ontario Science Centre with presentations about the potential for the river's rebirth attracted hundreds of people interested in cleaning up the Don.

As part of an environmental push at city hall, then city councillor Jack Layton announced, "'We're convening a group of citizens down at city hall, so come on down,'" recalled Mark Wilson, who later became chair of the group. "So I did."

Marie Day, who was also at the Science Centre event, said she played in the Don River when she was 10, decades before the Don Valley Parkway ran through the Lower Don, collecting fossils with her siblings and swinging on nearby sumac trees — like her father, former ɫɫ�� mayor Ralph Day, who also played in the ravine as a child.

"I didn't realize that it was being used as a dump," she said about why she took up Layton's offer. "I remember (as a kid) we actually found a salmon in the river … all these creatures were desperately trying to hold on."

Soon after, 20 citizens ranging from architects and historians to activists and cartographers, and three city councillors formed a task force to figure out how to clean the polluted watershed and help ɫɫ�� see what the Don was and what it could be.

The group's ideas included recruiting volunteers, planting trees along the lower Don Valley and convincing high-profile corporate representatives to do the same.

But, "as we looked at the physical river, it became obvious you needed to do something more dramatic to bring back nature" than just de-polluting it, Wilson said, noting the river was inaccessible south of Riverdale and only became natural north of Gerrard. "How do we bring the natural river north of Gerrard to the south?"

The efforts evolved into today's massive restoration project, but it meant years of fighting naysayers and convincing politicians through smaller projects, such as revitalizing Chester Springs Marsh along the Lower Don Trail.

It also meant generating publicity and engaging the public: "We'd invite children to come down and walk along the Don trail," said Day. "Their parents would send angry letters saying, 'oh, my kids running shoes got soaked.'"

Sketching the vision

By 1991, the task force was an official city committee and its first report titled "Bringing Back the Don" hit council floor that summer. It was the first time anybody sketched a vision to reclaim the mouth of the river by rerouting it through the Port Lands, Wilson said.

Most thought the idea was "amazing, inspirational," he said, but also "there was this, 'You guys are nuts. This is totally impractical' from the technocrats and the bureaucrats."

That fall, a "pivotal" and "emotional" moment legitimized the idea, according to Wilson. During public consultations for the , Wilson and Paula Davies, another member of the task force, played a recording of opera singer Mark DuBois' "Come to the Vale of the Beautiful Don" during their pitch to redirect the river.

It captured the imagination of the head of the commission, former ɫɫ�� mayor David Crombie. He ended up making the Don regeneration the centrepiece of his report.

The idea then became a question not of "if," but of when and how, said Wilson.

Around that same time, the Port Lands idea got a big boost from an unexpected source.

On an unrelated trip to ɫɫ��, a 42-year-old Prince Charles was looking to support a community group advocating for the environment.

"Crombie and the gang recommended us," Wilson said, who ended up giving Charles a personal tour of the area. "Suddenly we had all the glamour of royalty supporting the Don regeneration."

But there were still the logistics — including the cost — of getting it done, which were daunting, Wilson said.

It would be another decade and a half before the vision inched closer to reality. The city held an in 2007 requiring four teams to give the Don "an iconic identity" in a "bold and comprehensive" design for the river mouth that protected the area from flooding, restored the habitat and integrated development.

These ideas on paper were brought to life by competition winner Michael Van Valkenburgh Associates (MVVA), a U.S. landscape architecture firm whose vision for the Port Lands included new parklands, a new island, a new river valley that can carry large volumes of stormwater — and the Don Greenway, another outlet for the Don during heavy floods.

When presented with what seems like an impossible task like redirecting a major river through Canada's largest city, "you hedge your bets," said Laura Solano, project director and partner at MVVA. "You surround yourself with people that can tell you whether or not your idea is even possible, and if so, how to make it enduring and graceful."

Fighting the Ford factor

Then, suddenly, politics nearly upended the whole project in 2011.

During his brother Rob's mayoralty, then-councillor Doug Ford announced on a radio show an alternative vision for the mouth of the Don because the accepted plans were taking too long: seize control of the Port Lands and build a monorail, a megamall and the world's largest Ferris wheel. A Star editorial then called it a "blatant waterfront cash grab."

It blindsided almost everyone.

Coun. Paula Fletcher (Ward 14, ɫɫ��-Danforth) said it was the "most tumultuous" time in her 21 years on council, noting the Ford brothers' proposal was developed with external architects and developers in private, without council's approval or public input.

"We were going to grit our teeth and fight like hell," said John Wilson (no relation to Mark), who was chair of the Don task force when Rob Ford dismantled it just months before Doug's announcement.

Some dozen task force members spontaneously formed a new group that worked around the clock collectively, said Wilson, meeting with councillors, sitting around kitchen tables and board rooms after hours.

After two weeks of press conferences, spilled ink and a public uproar, city hall was inundated with thousands of letters, emails and signatures on petitions begging council to not "sell out our waterfront" for a "collection of ideas developed by an untested agency in the back rooms."

In the end, council voted unanimously to scrap the Fords' plan but called on Waterfront ɫɫ��, the tripartite agency overseeing the project, to speed up development as a compromise.

The mouth takes shape

After money from the three levels of government started with $65 million in 2016, the first phase of construction began with the realigning of Cherry Street. The following year, $1.25 billion was allotted to the project, and Waterfront ɫɫ�� began preparations to break ground on the new river valley.

Between 2017 and 2018, Herb Sweeney, principal at MVVA and team captain for the project, said "a game changer" moment came when they visited Rouge River trying to understand the landscape there relative to their designs for the Don.

Initially they planned for the Don to empty into the lake in a curved L-shape. Rouge River made them realize that shape was "vastly insufficient" to allow enough space to build wetlands and match what was in other river mouths, Sweeney said.

Instead, making the river valley curve more would thicken and widen the wetlands bordering it, strengthening the available surface area into larger, more contiguous wetlands which better serve its necessary functions including habitat creation and stability in case of floods — exactly what was needed at the mouth of the Don.

So, they changed the river valley into more of an S-shape, Sweeney said, "immediately increasing the habitat value" and allowing a "rich, robust foundation for four large new wetlands."

Marshes act like filters and restoring them around the new mouth of the Don meant water that left the river through those wetlands would also come out cleaner into the harbour.

Digging in the dirt

After settling on the valley's shape, the next step was figuring out soil conditions. If workers were going to dig up a Rogers Centre worth of dirt, they had to know how badly it was contaminated, whether it could be repurposed once cleaned — and how stable its foundation was, said Steve Desrocher, Waterfront ɫɫ��'s director of soil and groundwater management.

"You have materials like concrete, brick, rubble, household waste, glass bottles and things like that mixed into (the soil)," on top of a long legacy of industrial activity, said Desrocher.

Workers looked at everything — from a that posed as the watershed's report card to fire insurance maps from the late 1800s.

But most important were the thousands of soil samples taken from the roughly 500 holes workers drilled into the ground, samples sent to a laboratory for chemical and physical analysis. This gave an idea of where and how bad the contamination was — and whether the soil should be sent to landfill or cleaned up before being reused.

To do this for every square inch of the site would take forever and be too expensive, said Desrocher. So using the samples and their lab results, workers created a reliable 3D computer model that predicted what the soil would be like at any given point.

"When we start digging, we use that blueprint to separate out those soils," said Desrocher. Excavation and construction of the river valley started in late 2020 and continued, in various phases, until early 2024 when it was filled with water.

While the techniques aren't rare, "it's not common for it to happen at this level of detail over this scale," he added.

About 65 per cent of the roughly 1.5 million cubic metres of soil excavated from the river valley was reused in the Port Lands, such as at the parks, while 35 per cent was sent to landfill.

Almost half of the soil that was reused did not require decontamination, while less than one per cent was subject to intense heat in custom-made steel boxes like giant ovens (called thermal remediation) and 16 per cent was oxygenated with various nutrients and compounds (bioremediation).

With bioremediation, "we're trying to increase the digestive rate of the microbes that are in the soil naturally," said Don Forbes, Waterfront ɫɫ��'s project director overseeing remediation and earthworks. "So we're adding nutrients, surfactants, moisture, oxygen to that soil to keep the microbes consuming the hydrocarbons that are the contaminants in the soil, like residual oils and gases."

All of this soil remediation, given the volume, "played an important role in our ability to reuse it, divert it from landfill and manage costs," said Forbes. "It also meant we had to import less soil."

Down in the valley

MVVA's Sweeney compares carving out the river valley to building a bathtub — it needs barriers to keep the excavation area dry and stable. After all, it's bounded by the Don River to the north, Lake Ontario to the south, ɫɫ�� Inner Harbour to the west and Ashbridges Bay to the east.

So the river valley was temporarily sealed off from ɫɫ�� Harbour, the Keating Channel, and the Shipping Channel using concrete walls, or plugs, leaving the construction site relatively dry, allowing them to use conventional methods, such as a bulldozer, to carve the river valley in the "most cost effective, efficient and expedient" way, said Sweeney. Construction in a wet area would require extra work and more complicated machinery.

Vertical walls along the entire length of the valley on both sides keep contaminated soil and groundwater out, while protective horizontal barriers at the bottom of this "bathtub" keeps contaminated groundwater out.

If contaminants get through these "impermeable, durable" barriers, Forbes said, there is another barrier made up of grains of gravel coated with bentonite (a highly absorbent, viscous plastic clay) and carbon-activated layers, like filters, to absorb them.

The river valley's proximity to Lake Ontario and the elevated groundwater meant workers had to install an underdrain system beneath the "bathtub" as well. This pumped water from underneath the valley to an on-site treatment plant and tossed that clean water into the lake during the digging. It also prevented the environmental barrier and river finishes from popping out of the ground before the river water was reconnected above.

"We couldn't remove all of the contaminated soils out of the Port Lands — that would've just been impossible, costly and irresponsible, to do," said Sweeney. "By creating that barrier, we're able to then bring stones, boulders, wood, planting soils and plants (above it) … to stabilize the river channel bank (when water is poured into it)."

So how are the lands and parks around the river valley able to survive if not all of the soil was decontaminated? A different, and more simple, environmental barrier was used. On top of it, workers dumped piles of scooped and cleaned soil (which once sat at the river valley site) to physically raise the parklands above flood levels.

"There is a three-foot layer cap on top of the contaminated soil that is made up of clean soil," which keeps contaminants from migrating, said MVVA's Solano.

Building bridges

With the river valley cutting across a massive piece of land, the portion north of the river valley (south of the Keating Channel) becomes an island — informally known as Villiers Island, Indigenous elders recently proposed naming it Ookwemin Minising, meaning “place of the black cherry trees.”

That island, which will be developed into a new neighbourhood, requires new bridges and streets.

In fact, roads were worked on even before the river valley was dug up. First, workers had to shift Cherry Street so they could build the western temporary wall, removed this summer, that helped keep water out of the river valley construction site.

So the street was shifted a bit to the west and the new Cherry Street South Bridge built over the Polson Slip. The street now extends north over the Keating Channel, through the new Cherry Street North Bridge (the old one was demolished) and onto the mainland.

The newly opened Commissioners Street Bridge connects the island and the east downtown shoreline.

Shannon Baker, Waterfront ɫɫ��'s project director overseeing parks and public realm, said these three bridges — "architectural icons" painted red, yellow and orange on the inside — are also landmarks for the parks opening next year.

"When they're open, you'll always be able to orient yourself within the river valley system," said Baker.

Co-ordinating a whole host of construction sequences for the streets, river valley and parks was "one of the major challenges because everything impacted something else," added Baker.

Watching the river flow

By February this year, the river valley was ready to be filled with water after a year's worth of meetings, inspections and "a long list of what we need to think about," said MVVA's Solano. That included making sure the river slopes were stable, inspecting the environmental barriers, getting final approvals from regulatory agencies and preparing contingency plans for the possibility of winter bringing ice floes.

"Commissioning a building is normal. Commissioning a river is rare," said Solano. "You can't just Google it."

This meant devising a game plan for how workers would eventually remove the three temporary walls holding back the surrounding water.

"You have to hydrostatically balance the river level with the level of ɫɫ�� Harbour and the Don River," said Solano. "So there were some careful calculations about that relative to how fast can we fill the river? How long does it take?"

The west wall was essentially a dam to hold back Lake Ontario during construction, Sweeney said. Earlier this year it was sliced, partly under water, with a wire saw and scooped out in pieces.

The south wall near the Don Greenway was significantly smaller, with a gate to keep carp and other big fish out of the wetland, while protecting the habitat and allowing "desirable fish" to enter and spawn, Sweeney said.

The north wall near Villiers Street, the latest removed, was constructed differently. Up until Nov. 8, workers had been grinding away at the wall and the steel beams holding it up.

A sign of hope

For decades, the Don's task force had to persuade multiple cycles of mayoral administrations, prime ministers and provincial dignitaries that the project was worth completing. "It doesn't just happen by magic," said the task force's Mark Wilson.

John Wilson, who joined the group in 1994 and later became chair, said he thought at the time re-naturalizing the mouth of the Don was "a pipe dream 50 years out."

For him, balancing nature with civilization and intensification, concepts that rarely go hand-in-hand in dense urban settings, is "a sign of hope that we're not doomed."

The restoration of the Don River, he said, means "humans don't necessarily have to be a plague on the environment."