What lies beneath Lake Ontario

Patchen Barss
photo of light underwater

For a time, it seemed Torontonians had collectively forgotten that their city was at the edge of a Great Lake. That’s slowly changing, but many downtowners still go for months without a glimpse of the waterfront.

Further east, though, Toronto is experiencing a renaissance as a lake-facing metropolis.

From the mouth of the Don River to the far edge of Scarborough and even beyond, boaters, beachgoers and bathers are embracing their waterfront as an integral part of everyday life.

Meanwhile, at U of T Scarborough, researchers are discovering new secrets about this stretch of inland shoreline.

Here are a few things lurking in Lake Ontario that you might not know about:


It may come as no shock that there are fish in the lake. But who knew they’d be quite so appetizing?

“Lake Ontario is an underutilized fishery with lots of good places to go fishing,” says UTSC alumna Katherine Hills, who has “pulled huge bass and huge pike” out of the lake. Hills, who did her Bachelor’s degree in Environmental Biology and a master’s in Environmental Science at UTSC, says the Toronto and Region Conservation Authority (TRCA) has just created a list of good fishing spots.

Hills works at the TRCA, monitoring fish communities, water quality, invasive species and other factors that infl the quality of Toronto’s waterfront, especially as it pertains
to fish habitats.

She spends two weeks each summer and two weeks each fall “electrofishing” near the shore of Lake Ontario. A special flat-hulled metal boat acts as a cathode, and Hills’s team swing anodes out in front of the boat. When the anodes touch the water, they create an electrical current that stuns fish.

“We do species identification and log weights and lengths,” Hills says. “We tag big sport fish and record other information. We see species at risk like the American eel, alongside invasive fish like the goby and carp.”

Hills’s research connects to fish-habitat monitoring. As Toronto’s waterfront develops, the preservation and restoration of fish habitats is an ongoing concern.

"From the fish community surveying we do, we see a difference," says Hills. "Where you've got more diversity of habitat, you see more diversity of fish."


Theoretically, the Great Lakes have tides. But the moon and sun never change the water level by more than a few centimetres. Much more influential are seiches, long-wavelength swells that bounce back and forth across the water, changing water levels in a rhythmic cycle. Seiches are propelled by wind or variations in air pressure.

“Big basins have a period similar to a tide, but not driven by the moon,” says Professor Mathew Wells of UTSC’s Department of Physical & Environmental Sciences. “In Toronto Harbour it’s one hour, during which the level goes up and down by about five centimetres.

“Seiches cause water to flow into and out of the harbour,” the fluid dynamics expert explains. “It’s like the lake is breathing.”

Understanding the ebb and flow of the lake provides crucial information that informs waterfront development and renewal.

“When water moves slowly, it creates greater temperature differences,” Wells says. “A lot of fish need warm-water habitats, and there’s not a lot of that in this part of Lake Ontario. So we’re trying to come up with designs that allow for more.”

Seiches, of course, are just one factor in how water moves around in the lake. In Pickering, Wells has been studying the transition layer called the thermocline—where warm surface water meets colder deep water. Wells has found that the thermocline can move up or down by 15 or 20 metres in a single day.

Fish tend to prefer a more consistent temperature, but Wells has found other organisms that embrace the zone where temperatures shift quickly and regularly by as much as 10 degrees.

“We found out that a weed called cladophora and most of the zebra mussels are growing in this region, where the thermocline is moving up and down,” he says. “You can’t see it unless you put a measurement down. That’s where a lot of the life is.”


George Arhonditsis, chair of the Department of Physical & Environmental Sciences, has an ocean of data about Toronto’s Great Lake.

His statistical models connect the dots between environmental contaminants, fish habitat quality, fish populations and human activity.

The models help predict how new policies might affect the integrity of Toronto’s lakefront systems. Also, because economics are factored in, they show how people can best profit from this great natural resource. 

“If we could increase the fish population in Lake Ontario by 15 per cent,” Arhonditsis says, “and that’s not a hugely ambitious target, the economic benefits would be between $3 and $6 million.

“Even more impressive,” he adds, “if we could achieve just 11 fewer days each year when beaches were closed [due to pollution], it would create $40 to $75 million in total economic benefit.”

Arhonditsis has conducted surveys and research to see what people know and how they feel about their lake. He is pleasantly surprised to find they are largely up to speed.

“They know things are improving, and that the government has invested billions in the state of the lake.” Better yet, he says, people tend to see that investment as good value. “They are willing to spend a decent amount of money—money that comes from their own pockets—to improve water-quality conditions.”

Arhonditsis’s statistical models help generate maximum return on that investment.

“Modelling allows you to identify cause-and-effect relationships,” he says. “It allows you to build mechanistic understanding of how nature operates. It also allows you to project future responses and test ‘what if’ scenarios: What if you reduce emissions by 30 per cent? Or by 35 or 40 per cent? What effects will that have?”

When working with policy makers, Arhonditsis is always careful to highlight the limitations of his models.

“Part of my group’s job is to communicate uncertainty and make sense of it,” he says.

Lake Ontario is an “open system” that is continually changing, and even the most sophisticated models rely on incomplete data.

This means that for researchers, and for all Torontonians, the lake may be offering up surprises for years to come.