Manitoba has finished a unique experiment to kill off zebra mussels in four of its harbours.

The province sealed off the harbours with a silt curtain before injecting liquid potash into the water.

Zebra mussels, an invasive species, were first spotted in Lake Winnipeg in October 2013, according to the provincial government. Manitoba recently declared victory in its first battle with zebra mussels. (CBC) Conservation Minister Gord Mackintosh said the treatment was successful and killed the mussels.

"I'm pleased to announce what we have dubbed 'operation mussel out' has been a success," said Mackintosh.

The province said no mussels survived the treatment, but so far Mackintosh is holding back declaring Lake Winnipeg a zebra mussel-free zone.

He said that was just the first step in the battle to keep the mussels out of the province.

Mackintosh said there is still a good chance zebra mussels are still lurking in the water outside the harbours.

He said Manitoba is increasing monitoring on Lake Winnipeg and the province now has five decontamination units for boats that could spread the mussels.

"It's wonderful to be monitored. I'd give the province an "A" for effort,” said Robert Kristjanson, a fisherman on Lake Winnipeg. “It's just that they should have done it a long time ago."

Kristjanson worried the province was too quick to claim victory on a problem that has plagued lakes across Canada.

"You shouldn't be too optimistic that this has solved anything, because there isn't anywhere in Canada, including the Great Lakes, who have found a solution to this problem."

The invasive species, which is already in the Great Lakes and has spread throughout parts of the United States, was found for the first time in the province last October.