Ancient rivers, ice sheets and then locks and dams were the key players.

Peterborough Examiner  – November 25, 2023 – by Drew Monkman  

It’s hard to over-emphasize how fortunate we are in the Peterborough area to have such a wonderful chain of clean, beautiful lakes right on our doorstep. It’s easy to take them for granted. I remember that when I lived in Quebec City and later in Edmonton, the absence of easily-accessible, high-quality lakes was one of the things I missed the most. But how much do we really know about our lakes? How were they formed?

The Kawartha Lakes are the headwaters of the Trent River system which drains into Lake Ontario. They include Balsam, Cameron, Scugog, Sturgeon, Pigeon, Little Bald, Big Bald, Buckhorn, Chemong, Upper Chemong, Lower Buckhorn, Lovesick, Stoney, Clear, Katchewanooka and Rice. There are also many other smaller lakes such as Sandy, Coon Lake, and Big Cedar, and the many lakes that make up Kawartha Highlands Provincial Park.    

Clockwise from top left: Granite on north shore of Stoney Lake at Burleigh Falls; limestone cliff near south shore of Lovesick Lake at Burleigh Falls; limestone cliff along Otonabee River; standing inside a giant kettle at the Warsaw Caves; dams and locks totally transformed the Kawartha Lakes (Drew Monkman photos)

Shield-contact lakes  

If you look carefully at a map of the Kawarthas, you’ll notice that the more northerly lakes – Stoney, Lovesick, Lower Buckhorn and Bald – follow an irregular east-west orientation along the edge of the Canadian Shield. On the northern shores lie hard, ancient Shield rocks such as granite. On the southern shores, we find limestone. The lakes essentially lie in a groove or valley at the junction of the limestone and Shield rock types. Well before the first glaciers, the initial valley probably formed as a result of a river or river system flowing east along this junction. The flowing water found it much easier to cut down and southward through the relatively soft limestone than through the extremely erosion-resistant Shield rock on the northern shore. This erosion deepened and widened the lakes.   

A curious feature in areas of the southern shorelines of Stoney, Lovesick and Lower Buckhorn is the presence of limestone cliffs, some measuring 30 metres high.  An excellent example can be found along the south shore of Lower Buckhorn Lake, off of Millage Road. The presence of the cliffs is connected to the nature of the limestone itself, of which there are two kinds – a layer of strong, more erosion-resistant limestone lying on top of a weaker, softer form of the rock. Millions of years ago, these layers were uplifted by the movement of the Earth’s tectonic plates and now angle slightly downward to the southwest. Because of this angled uplifting, part of the lower, weaker bed of limestone was brought to the surface. It is this layer that makes contact with the Shield.

The weaker, Shield-contact limestone bed is the layer that was eroded by the ancient, eastward-flowing rivers described above. However, as the river cut laterally and southward through this softer limestone, the harder bed of limestone lying above it was eventually undermined by the water. Large blocks of this harder variety eventually broke off and came crashing down into the valley below.  The end result was a steep, cliff face of limestone that faces north. Niagara Falls was formed in much the same way.   

The more southern lakes

The other large Kawartha Lakes such as Clear, Chemong, Buckhorn, Pigeon and Rice occupy valleys that were cut into the Ordovician limestone bedrock by ancient rivers. The valleys lie on a northeast – southwest orientation which is the same orientation that the glaciers followed.  These ice sheets deepened the valleys as they moved southward and also left behind thick deposits of rock, gravel and sand on the uplands between the valleys.     

Of special interest is Sandy Lake, located just west of Buckhorn on County Road 37. The first thing you notice is its slight turquoise colour. The lake bottom is different, too. It is made up of soft, white “marl”, a mixture of silt, clay and calcium carbonate. Sandy Lake is also unique in being totally spring fed and usually clear of turbidity. The turquoise colour results from the minerals present in the surrounding limestone and carried by the springs into the lake.

The drainage system   

            The water draining into the Kawartha Lakes comes largely from the Canadian Shield through tributaries such as the Mississagua River (drains into Lower Buckhorn Lake) and Eel’s Creek (drains into Stony Lake). However, a few rivers that feed the lakes flow from non-Shield origins and drain the low-lying areas of limestone bedrock and glacial till in the southern Kawartha region. For example, the Scugog and Pigeon rivers actually flow northwards into the lakes of the same names; Jackson Creek flows eastward from the Cavan Swamp into the Otonabee River; and the Indian River flows into Rice Lake but actually delivers water from Stony Lake.

The Indian River is famous for the Warsaw Caves. The caves were formed by the flow of glacial meltwater when the glaciers began to retreat 12,000 years ago. The ancient Indian River was very different from the shallow, placid river of today, being more like the modern-day Niagara River. The deep, swift, glacier-fed river shaped the landscape found within the Warsaw Conservation Area leaving behind caves, kettles, and limestone cliffs.

The lakes have changed

If it was possible to travel back in time a couple of hundred years, the first thing you’d notice is how much smaller the lakes used to be. This is especially true for Chemong, Pigeon and Clear. Because of the need for water power and transportation links between the various towns and villages, dams and locks were built in what was to become the Trent-Severn Waterway system.  The highly-controlled water levels made these lakes both deeper and wider. What were once simply low-lying forests around the perimeter of the original lakes are now shallow bays, often full of submerged logs and tree stumps. 

Maybe the least recognizable body of water in pre-settlement times, however, would have been Rice Lake. Huge beds of wild rice grew around the perimeter of the lake and were harvested by native people. They also attracted multitudes of waterfowl. The beds were destroyed, however, when the dams and locks caused water levels to rise.   

The Otonabee River was unrecognizable, too. Before the construction of the waterway, the stretch of the river between Peterborough and Lakefield was characterized by extensive sections of rapids. They were a huge obstacle to transportation. Rather than carry their canoes around the many rapids, local native peoples and the first Europeans often preferred to take the portage route that used to run between Little Lake and Chemong. As for Lake Katchewanooka, it was little more than the upper section of the Otonabee River.  

The next time you’re out for a drive or boat ride in lake country, keep in mind how our heritage of lakes and rivers was formed and how much these waterways have changed.


Alarm: The world is on pace to warm by as much as 2.9 C by the end of the century, according to a new United Nations report. Large parts of Earth are at risk of becoming uninhabitable and extreme weather events could increase tenfold. Only if countries achieve their most ambitious targets — cutting net emissions to zero by around 2050 — can warming be held to even 2 C. However, most countries haven’t yet underpinned those targets with legislation and implementation plans. Global greenhouse gas emissions are actually at a new record high. According to another report, Canada is expected to fall short of meeting its 2030 greenhouse gas reduction target. There appears to be little appetite among Canadians to change their behaviours in order to make hitting this and other reduction targets a reality. We can’t even abide a revenue-neutral carbon tax.

Carbon dioxide: The atmospheric CO2 reading for the week ending November 18, 2023 was 421.22 parts per million (ppm), compared to 417.31 ppm a year ago. As a result of quickly rising CO2, 2023 will almost certainly be the warmest year on record. 

Drew Monkman

I am a retired teacher, naturalist and writer with a love for all aspects of the natural world, especially as they relate to seasonal change.