Warm water and Great Lakes salmon. Do they mix?
Salmon run: Will the warm Great Lakes have an impact on the fish?
The river water was not nearly as cold as I thought it would be, and given the early October date, that felt weird. This warm, this late in the season? Was this warm water going to have an effect on the fish?
As I waded out into the heart of the shallow river, the slippery rocks gave way to soft sand, and dark shapes flashed through the water. Fish or waving strings of algae? I couldn’t easily tell, but I knew that salmon were swimming somewhere close, and they aren’t small fish.
A fin broke the surface, and, in a moment, I realized I was seeing a school of Pacific salmon in a scene that was more reminiscent of the west coast rather than the waterways of the Great Lakes. This is a scene that has been occurring every fall for years, and although I had heard about it, I had never had the opportunity to witness it firsthand.
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What immediately came to mind was, “Is the warm water affecting the salmon heading upriver?”
The salmon run is a phenomenon that happens every year in the early to mid-fall; late September to mid-October is the usual time. It’s mostly confined to Lake Ontario, and because of that, the rivers in the Greater Toronto Area (GTA) are their favourite waterways to swim up.
Timing is one of the most popular questions that the Toronto Region Conservation Authority gets, and 2025 is no exception. However, this year is a bit unusual given that Lake Ontario is above the average temperature and there’s been an ongoing drought throughout southern and eastern Ontario.
Having the same questions as much of the public, I decided to talk to the TRCA to find out what we know about the salmon run.
I got ahold of Colin Love, TRCA Supervisor of Community Outreach and Communication, and asked him a few questions about the phenomenon. My first impression of him was how passionate he was about the sheer magnificence of the salmon run.
One of my first questions I asked was about the species that make the run, and the answer surprised me: “First and foremost, the species that would have been making this run, the Atlantic Salmon, are locally extinct from back in the 1800s—that’s due to fishing and habitat loss. The good news is that in the recent decades, there’s been a great effort to bring back the Atlantic salmon. However, the vast majority of the salmon we see here are Pacific species, mostly Chinook and sometimes Coho, species that are more associated with the West Coast of Canada.”
The two groups of fishes have slightly different lifestyles with the Atlantic salmon making the run up the rivers to breed and then returning to the ocean more than once. Pacific salmon make the run once and then die, becoming an important part of the nutrient flow back to the land, even here in Ontario. So, yes, you will see dead salmon in the upper reaches of rivers like the Humber and that’s completely normal and expected.
“The Pacific species have adapted to the Great Lakes fairly well, and we’ll see them swim many kilometres upstream, all over the TRCA’s jurisdiction. It’s incredible to see these fish beat all odds and make leaps over natural and constructed barriers, especially in the GTA.”
Timing is, of course, another big question, and I wanted to know if October was too late to see them. Colin reassured me that there was still time.
“It’s a question that often humbles us, scientists and nature enthusiasts alike, because we often don’t know when this phenomenon is going to happen. We think it’s based on water temperature, which is in turn based on rainfall and seasonal changes. It tends to be from later in September into October, but things can shift.”
Which brought me to a big question for 2025: are we seeing a significant shift due to warmer weather and lack of rain? Colin cautioned that we don’t have good data just yet. “We’re still a little early in the season to really know much about the numbers just yet. They’re coming now, but we just don’t want to say that we’ve seen the peak yet.”
So, if there’s still time yet to see the salmon moving up the river, I asked where the best viewing spots were.
"It’s right in our backyard!," said Colin. "There are a few hotspots: Etienne Brule Park right around Old Mill on the Humber, Morningside Park in Scarborough, and the other rivers as well. We’ve got an excellent tool in our observation map on our website. It’s a great way to report sightings and see where they’ve made it to you."
One important question is, of course, can you fish for them? Colin cautioned that TRCA doesn’t make the rules around fishing regulations and to check the Ministry of Natural Resources website.
“For any regulations, check the provincial authorities, but one thing I can say is that thinking about these incredible animals completing this journey, what an incredible, humbling moment for us as people to step back and observe. We can actually help them on their migration both upstream and down. That might mean curtailing pollution, recreating and protecting habitat, or figuring out what to do with our stormwater.”
“Finally, I’d love to encourage everyone who is interested in the journey that these fish are taking to come and see and understand this incredible, beautiful natural phenomenon that’s taking place right in our backyards.”
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(Header image: Héctor Berganza/Pexels. File photo used for illustration purposes only.)