Much of southern Ontario has an inclination to drain to the southwest. Prior to the last glaciation, there were many valleys that were roughly parallel. The shapes of the Kawartha Lakes today reflect this former drainage network.

About 20,000 years ago, the Ice Age was at its peak and southern Ontario was buried under a giant sheet of ice that stretched from the Rocky Mountains to New England, and south into the upper Mississippi Valley. At its peak in Nunavut, Laurentide Ice Sheet was over 3 kilometers thick, and even as far south as Manhattan it was 600 metres thick.

The accumulated ice in the Laurentide Ice Sheet was so heavy that it moved under its own weight. In southern Ontario advanced one that followed the Great Lakes (gouging them out as it passed) and another that advanced from the North. They met about 20 kilometres north of Lake Ontario. As they advanced they bulldozed the ground ahead of them and when they converted this formed a ridge of sand and stone, known today as the Oak Ridges Moraine.

As the glacier slowly retreated, it left behind a massive pool of meltwater. Glacial Great Lake Algonquin encompassed the basins of Lake Simcoe, Lake Huron, Lake Michigan and Lake Superior. The Oak Ridges Moraine was blocking the previous drainage valleys, but the water had to find some way to drain. As the valleys overflowed, the currents carved new spillways, ultimately creating the Kawarthas Lakes. It was a circuitous route, bypassing the moraine to the east.

For a brief period, Fenelon Falls controlled the height of Great Lake Algonquin. The deluge of water pouring over the falls carved the Fenelon Gorge through the limestone sheets, and the falls ultimately worked their way upstream to their present location. The great volume of water meant that the waterway was wider than at present. As the river retreated into its present banks, it left behind severely eroded shores, that were not capable of supporting dense forests. The ancient bur oak grove [Hyperlink to forthcoming exhibition on the Oak Grove] is one example of the unique ecosystems that resulted.

As the glacier retreated north from southern Ontario, a large block of ice broke off and melted in place. As it disintegrated it dropped a massive amount of stone, sand and gravel. This created the Dummer Moraine, which is about 13 km wide and 200 km long, stretching from Coboconk to Sydenham. The moraine is very stony, rolling land, though good soil has since developed in scattered pockets.

After the ice sheet melted, southern Ontario was a vastly different environment than what exists today. It was much colder, and much of its topsoil had been scraped and eroded away. Plants, trees and animals that had weathered the ice age to the south, began to recolonize. The first trees to arrive were spruce, fir, tamarack and jack pine, within about a thousand years of the glaciers retreat. Pine, hardwoods and hemlock followed. As forests re-established themselves in the region, their leaf litter decomposed to create soil.

It did not take long after the glaciers retreated for the first humans to reach southern Ontario. They seemed to have some association with large game, including mastodon. At about this time, the populations of these large animals declined precipitously, as part of a major extinction event across North America.

In the millennia that followed, the forests moved towards new equilibriums. Forests evolve through a succession of species, with sugar maples and hemlocks tending to dominate in mature forests. One notable event, was a significant decline in Hemlock forests about 4000 years before present across a large portion of eastern North America. On the eve of settlement, the most common forest tree was the sugar maple.

At the start of the nineteenth century, the most common tree in the upland forests was the sugar maple, often occurring together with basswood, white pine (red pine was less common) and hemlock. In lowlands, cedars were the most common trees, and tended to occur in separate stands from tamarack. Birch, alder and soft maple were also common. Elm was the sixth most common genus, and occurred in a great variety of locations, both lowlands and uplands.

As the forests were evolving so too was the watercourse. While the volume of water passing down the Trent was many times larger than at present shortly after the glacier retreated, it settled into an equilibrium that was much lower and more irregular than at present. The Kawarthas that we know today, require a lot of hydrological engineering to maintain the present lake boundaries and stable water levels.

Many reservoir lakes further up the watershed are filled with water in the spring that can be let down to artificially maintain the water levels and navigation. In its natural state, the Trent Waterway had large seasonal fluctuations. Little Bob Channel at Bobcaygeon, for instance, was intermittent, with substantial flow in spring, but dry in summer. Most lakes along the waterway were several feet lower than at present, and there was typically little depth to the water passing over the falls or rapids.

The lakes along the Trent Severn Waterway today are at least 5 feet higher than they were in the early nineteenth century. Mitchell and Canal Lake were a creek draining into Balsam Lake before the water levels were raised. The waterway was designed to accommodate boats drawing up to 5 feet of water, and it was easier to dam and raise the lakes than blast all the obstructions between the lakes out of the way.

Damming also allowed water level management. Cameron Lake is a deep bowl, so its boundaries were not as profoundly altered as Sturgeon Lake. There is a particularly large area of drowned land on the southern arm of Sturgeon Lake, where the Scugog River and Nogies Creek diverge.

Today southern Ontario is mostly fields, fencerows and human dwellings, but this is really a reflection of the massive extent of landscape change over the past two centuries. In the year 1800, it was said that a squirrel could travel from one end of Ontario to the other without ever having to touch the ground.

Aside from wetlands and scattered ecosystems that would not support forests (like the Ancient Oak Grove in Fenelon Falls, the Carden Alvar, and the Oak Ridges Moraine), were densely treed. South central Ontario was unique in having a waterway, that was home to three Anishinaabe or Ojibwa villages that lived along the waterway, or Gamiing, [LINK to Exhibit: Gamiing] as they might say.