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How did the glacial Lake Iroquois shape Toronto’s landscape?

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Toronto skyline — Toronto An aerial view of Toronto's skyline with the CN Tower at center.

Glacial Lake Iroquois, which existed approximately 11,000 years ago, profoundly shaped the landscape of Toronto. As a massive body of water that stood about 130 feet (40 meters) higher than the present-day Lake Ontario, its recession left a distinct mark on the city's topography.

While the modern site of Toronto is characterized by its almost uniformly flat terrain, the influence of the ancient lake is visible 3 to 4 miles (5 to 6 km) inland, where there is a sharp rise of approximately 40 feet (12 meters). This feature represents the former shoreline elevation of the glacial lake. Following the lake's recession and the subsequent rise of water levels to their current state, the area was left with a marshy shoreline that eventually provided the fine natural harbour that became central to the city's development and strategic importance.1