Syncrude Canada now says at least 350 birds have died after they landed on one of its toxic tailings ponds in northern Alberta.

The incident comes less than a week after the company agreed to pay more than $3 million in fines after being found guilty of charges in the deaths of more than 1,600 ducks at another one of its ponds in 2008.

Syncrude Canada president Scott Sullivan said Wednesday the company is calling on scientists to find new ways to ensure such deaths don't happen again.

He said Syncrude had deployed its entire system of sound cannons and other deterrents to prevent the ducks from landing. He also said the company has set up extra flare guns and air horns, but they proved ineffective.

Sullivan said the company is working with the Alberta government to figure out what went wrong Monday. The company had suggested freezing rain tired the birds out, forcing them to land, so their deterrents were ineffective.

Originally the company said 125 birds died.

Alberta Environment Minister Rob Renner called the bird deaths "discouraging in the extreme."

Gillian McEachern, a program manager with Environmental Defence said the latest incident shows there is no way to safely store a billion litres of toxic waste.

"Governments need to step in and require companies to get rid of tailings ponds altogether," she told CTV News Channel Wednesday afternoon.

Federal NDP environment critic Linda Duncan also said it is time to shut down the tailing ponds.

With files from The Canadian Press