As well as facing shallow water, rocks, predators, human infrastructure and pollution, salmon must occasionally overcome extreme heat that sees some rivers reach temperatures of 30 C or higher. Luckily, nature provides some oases for these cold-loving fish, including cooler groundwater seeps, shady spots and deeper sections of river.

But with global temperatures rising and heat spells becoming more common, these naturally occurring refuges may no longer be enough. In 2020, PhD candidate Kathryn Smith and associate professor Barret Kurylyk at Dalhousie University in Halifax set about designing cooling stations of their own in various Nova Scotia rivers.

The system’s first test in June 2023 coincided with a heat spell, and Smith rushed down to the river to see if their design was a success. “I was super excited when I saw the salmon aggregations,” says Smith. The numbers of salmon continued to grow over the next three days. “I joked to Barret that they’re telling all their fish friends to come.”

Kurylyk sees opportunity for these cooling systems to be set up on both the east and west coasts of Canada — the next step is to scale them up. For the salmon, these cool spots could mean the difference between life and death on an already perilous journey home.