Cradling the city's harbour like an outstretched hand, the Toronto Islands are more than a place to escape the city – they are the very reason the city exists at all.

Always a gathering place for First Nations, John Graves Simcoe, the first lieutenant-governor of Canada, also recognized the benefits of a protected bay. He laid Toronto's nascent grid in a nook where the islands – then a peninsula – connected to the mainland in a vast marsh just east of the Don River.

The settlement was safeguarded with a garrison (Fort York) at the narrow opening of the bay to the west and a stone lighthouse at the peninsula's tip. As tensions simmered between Upper Canada and the United States, Simcoe named the point Gibraltar to evoke the protective force of the massive rock that guards the comings and goings from the Mediterranean Sea between Europe and Africa.

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But Toronto's Gibraltar is a far cry from its namesake monolith. The peninsula-cum-island, created from currents of sediment deposited in the lake from the Scarborough Bluffs and Don River, was – until Depression-era infill projects – a constantly shifting sandbar, changing shape and form with each season and storm.

Historic manipulation of Toronto's dynamic coastline has put the islands' beaches at risk of being washed away. Stabilization of the Scarborough Bluffs, cliffs created by erosion, and the filling in of marshes to create the Port Lands have cut the islands off from their replenishing sources of sediment. And the construction of the Leslie Street Spit has blocked what little sediment does end up in the lake. They are part of years of major waterfront projects done before the words "environmental assessment" entered the bureaucratic vocabulary.

"And if no action is taken, Gibraltar Point could sever into two within 20 years" says Ethan Griesbach, project manager at Toronto and Region Conservation Authority (TRCA).

As part of its natural shifting and changing, erosion has been documented on the Islands since 1879. Despite efforts to fix its form, significant shore damage in the 1970s led to the construction of seawalls near Centre Island, and in 2004, a major winter storm resulted in emergency dumping of recycled concrete at the island's south western tip.

This year – especially in the spring and summer – the effects of erosion have been dramatic. Where there once was a wide beach stretching into the lake, Gibraltar Point beach has become a thin strip of sand, the water continuously lapping at the groves of poplars and dogwoods and exposing their foundational roots.

"Last winter was mild, with less ice coverage to provide shoreline protection from seasonal storms," Mr. Griesbach says.

"It's all gone," says lifelong Island resident, Jimmy Jones, 83, who grew up in a home near Hanlan's Point when houses covered the entire island. "You were able to walk, at least, 200 yards out from our house to the beach and lake level. Now, the trees are dropping into the water. And it's getting worse."

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"Intervention is necessary," Mr. Griesbach says of the fine line TRCA has to walk between letting nature runs its course, and taking action. "Without intervention, you'd lose those inland wetlands and important breeding grounds for fish. Those habitats would be completely gone with a breakthrough."

Gibraltar Point is also a significant cultural site, beyond its role in Simcoe's defence strategies. It is a place of healing for First Nations, and has been recognized as such by subsequent waves of European settlers. It's where the Lakeside Home for Sick Children was located in 1883 to benefit from its fresh air, and is currently the home of Artscape Gibraltar Point, an artists' centre and event space whose resident artists are continuously inspired by their surroundings.

"Artists are drawn to the geometry of Gibraltar Point," says Shoshonah MacKay, a frequent resident-artist of AGP. "Turn west, and see the towers of Toronto, Etobicoke and Mississauga. Shift your body slightly east and be consumed by the currents of the oceanic lake."

Because of its importance, careful consultation was necessary before a proposed recommendation was agreed upon by the project's many stakeholders, including the TRCA, the City of Toronto, Ports Toronto, the provincial Ministry of Natural Resources, the federal Department of Oceans and Fisheries, residents and visitors to the islands.

Many of the stakeholders were concerned that a proposed breakwater would be an imposition – Gibraltar Point's beaches are some of the last parts of the islands that have not been altered by human activity.

"But without off-shore protection, augmenting the beach would be tremendously costly," Mr. Griesbach says. "You need some kind of breakwater to avoid the 30,000 cubic metres of sand you'd need to add every year."

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A balance was struck to preserve the last tract of wilderness at the edge of Canada's largest city. The final design involves a combination of artificially adding more sand, and an underwater breakwater that, while almost invisible, will protect the Island from erosion.

In 2016, City of Toronto confirmed funding of $13.5-million, with an erosion control project at Gibraltar Point to begin in 2017. But because more than five years have passed since the 2008 environmental assessment was approved, Ontario regulation requires an addendum to confirm that past findings remain accurate.

"It's an important place and we understand something has to be done," Mr. Griesbach says.

Warren Hoselton, the Toronto Islands' park supervisor and partner in the project, agrees. "Our beaches have never been busier," he says. "We don't need smaller beaches, we need bigger beaches."