Invasive zebra mussels found in Saint John River last year

A study found invasive zebra mussels in the Saint John River.

A research group found an early-stage zebra mussel colonization in the Saint John River (Wolastoq) in New Brunswick last year, with many of them located near hydroelectric infrastructure.

Zebra mussels, which are an invasive species that can quickly grow their population, were already established at Lac Témiscouata, Que., which connects to the Saint John River via the Madawaska River.

A 2025 survey by the Canadian Rivers Institute and NB Power found 22 adult zebra mussels at three sites along the river. Nineteen mussels were seen at the Mactaquac Generating Station and two were found at the Beechwood Generating Station.

“One zebra mussel was detected near the confluence of Belleisle Bay and the Wolastoq, marking the furthest downstream confirmed discovery to date,” a news release from the institute reads. “Colonization patterns appear to reflect local hydraulic and structural conditions rather than simple proximity to upstream sources.”

The institute says zebra mussel populations become difficult and costly to manage once they expand, making continued seasonal monitoring important.

“The current low-level colonization provides an important opportunity to take informed, proactive steps to better mitigate negative impacts to infrastructure and reduce the risk of spread to other waters in New Brunswick,” said Dr. Meghann Bruce with the institute.

Bruce says the institute is working with partners like NB Power, New Brunswick Invasive Species Council, and the Department of Fisheries and Oceans to figure out where in the river the mussels are growing most, adding residents can help by checking boats, docks and other infrastructure around water for presence of mussels.

Zebra mussels spawn when the water is 12 C and can lead to clogged infrastructure like dams and generation stations on water.

“Once they’re established there’s very little that can be done, especially in an open system. When they are on infrastructure, if it’s a closed system, there is chemical treatment. But obviously we’ve got a 673-kilometre-long river,” said Bruce.

With files from CTV’s Avery MacRae.

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