The Pickering nuclear power plant is killing fish by the millions.

Close to one million fish and 62 million fish eggs and larvae die each year when they’re sucked into the water intake channel in Lake Ontario, which the plant uses to cool steam condensers.

The fish, which include alewife, northern pike, Chinook salmon and rainbow smelt, are killed when they’re trapped on intake screens or suffer cold water shock after leaving warmer water that’s discharged into the lake.

The Canadian Nuclear Safety Commission has told Ontario Power Generation, which operates the plant, to reduce fish mortality by 80 per cent. And in renewing Pickering A station’s operating licence last month, the nuclear regulator asked for annual public reports on fish mortality and the effectiveness of steps OPG is taking to reduce rates.

“Quite clearly we were talking about a lot of fish,” says a spokesperson for the commission, adding that while the kill has been going on “forever,” environmental issues were only recently added to licensing considerations.

But while the requirement for regular reports is a “huge start,” says an environmental watchdog, OPG hasn’t done enough to stop what he calls the “biggest killer of fish on the lake.”

A 610-metre barrier net it has strung in front of the channel is insufficient because it’s removed in winter and “does nothing about thermal pollution and nothing about larvae and eggs,” says Mark Mattson, president of Lake Ontario Waterkeeper, a grassroots charity working to protect the health of the lake.

“This is important to the lake’s ecosystem — the birds and people who eat the fish, and the commercial fishery,” he said in an interview. “What a terrible precedent it is that one of the biggest public corporations can just ignore the rules for fish and fish habitat in Canada.”

Mattson calls the plant’s cooling system the worst of available technologies.

“It sucks in clean water along with fish, eggs and larvae, then spits it back at close to hot-tub temperatures.”

The combined thermal plume from Pickering stations A and B ranges from 150 to 800 hectares at the water surface year round, and 50 to 300 hectares at the bottom during cold weather, he said.

But OPG denies plant operations are having an adverse effect on aquatic life or habitat and maintains there’s no evidence that thermal emissions are killing fish.

The agency installed the net and is monitoring mortality rates and lake temperatures because “we’re always looking for ways to reduce the impact on the environment,” said spokesperson Ted Gruetzner.

After four months, it’s too soon to say how effective the net is, but already fewer large fish are being seen. Small swimmers can still get through.

Installed last October, the net was removed for the winter because of the risks to divers doing maintenance work, Gruetzner explained, adding that fish are less likely to enter the channel in cold weather.

Noting that OPG spends more than $1 million a year on habitat projects in the province, he said the operator will consider stocking the lake with fish to replace those killed.

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The nuclear safety commission told OPG in October 2008 to fix the problem, reducing mortality for adult fish by 80 per cent and for eggs and larvae by 60 per cent. Citing the company’s failure to protect the lake’s inhabitants, the commission called the fish kill “an unreasonable risk to the environment.”

The Darlington nuclear plant uses a different intake system that doesn’t draw fish in.