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Fraser River floodgates could be stifling salmon: study

There is little regulatory oversight when it comes to tracking or mitigating ecological impacts of river infrastructure.

Salmon returning to spawn in B.C.'s Adams River.

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Andrew S. Wright

Salmon returning to spawn in B.C.'s Adams River.

As researchers continue to study why salmon populations on the Fraser River have fallen to historic lows, two new studies show that floodgates on the river could be reducing habitat for fish — and there is little oversight when it comes to checking the ecological impact of that infrastructure.

“Past research in our lab had found that these floodgates were associated with low oxygen quantity in the creeks flowing into the Fraser through the floodgates,” said Rebecca Seifert, the lead author of a study by Simon Fraser University.

“They were seeing a dead zone where it was hard for sensitive fish like trout and salmon to survive.”

The floodgates reduce the flow of water, meaning more algae grows around the gates and lowering the oxygen level. Researchers have also found more invasive species and fewer native species near floodgates — and there are over 300 gates between Delta and Hope.

When the gates are closed, juvenile salmon can’t get out of the creeks where they were born to pass down the Fraser River and out to the open ocean, an important part of the salmon life cycle.

Seifert wanted to know just how often the floodgates were closed, so she installed timelapse cameras. She found that many of the gates, which close when high water pressure pushes them closed, are shut almost all the time during the high-water spring season. That’s also when juvenile season are trying to migrate to the Fraser.

Others open at low tide, creating an escape route for the fish.

A separate study by the University of Victoria and Watershed Watch found that there is a regulatory gap when it comes to tracking the impact infrastructure like floodgates are having on fish.

“We want municipalities, who often own and maintain flood infrastructure, to build it to be fish-friendly,” said Lina Azeez, a campaigner with Watershed Wach. “The technology exists.”

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