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How were the Kawartha Lakes Formed?

July 20, 2023

At the Southwestern tip of Rice Lake, the Oak Ridges Moraine can be seen rising in the distance on the south shore (right and background)

Looking at a map of the Kawartha Lakes, there are a lot of rivers and lakes, that seem to have channels that run from northeast to southwest—Balsam Lake, Sturgeon Lake, the Scugog River, Lake Scugog, Pigeon Lake, Chemong Lake, Clear Lake, Katchewanooka Lake and the Otonabee River. At first glance, it might seem like region’s natural drainage could have been on this axis. The watercourses would flow relatively directly towards Lake Ontario. In contrast, the actual course of the Trent Watershed takes a tortuous and winding route, eventually making its way to the great lake at the Bay of Quinte.

For much of the region’s history, its watercourses tended to follow these ancient river valleys. But at the end of the last glaciation, two main ice lobes met (Lake Simcoe and Lake Ontario—named for the basins which they filled… ice can flow overland if it is thick enough). As these great mounds of ice moved forward, they shoved great quantities of aggregate, and formed the Oak Ridges Moraine, about 16 kilometres wide, 160 kilometres long and 1400 feet high. It was roughly parallel with the north shore of Lake Ontario, about 15 to 20 kilometres back. Further north, a large block of ice was left behind as the glacier retreated. It melted in place, dropping the gravel, sand and boulders that form the Dummer Moraine, which runs from Coboconk/Fenelon Falls to Sydenham.

The aggregates deposited by the glaciers created massive dams, that blocked off river courses that had once drained the region. Instead of draining relatively directly southwest towards Lake Ontario, a new pattern had to form. As the glaciers were melting, there was much more water than there is today, carving the Fenelon Gorge, and many other channels between the lakes. As time passed, the region settled into the drainage pattern that we are accustomed to today—creating the Kawartha Lakes, which wound their way east to the Otonabee River and Rice Lake, then via the Trent River to Lake Ontario. The new watercourse ran between the two moraines, with much of present-day Haliburton County draining around the west end of the Dummer Moraine into Balsam and Cameron Lakes. Many smaller tributary streams flowed off this moraine into the lakes further east.

The beautiful landscape of the Kawarthas, with rolling hills ascending above the chain of lakes came together in this period. Verulam Township with its series of valleys, the drumlins around Peterborough, the Oak Ridges Moraine with its sparser tree cover to the south, and the chain of finger lakes all reflect this glacial history. The Kawarthas are a region with a varied landscape—much of it shaped by glaciation.

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