Potash experiment killed zebra mussels at infested harbour, officials say

Zebra mussels clustered on a small tree branch that had fallen into Rice Lake near Brainard, Minn, July 1, 2010. (AP / David Brewster)

WINNIPEG -- Manitoba says a unique experiment using liquid potash has halted a zebra mussel invasion in one of the province's harbours.

Officials say Winnipeg Beach will be reopened after it was closed two weeks ago. The harbour was one of four sealed off with a silt curtain and pumped with liquid potash until a lethal concentration for the mussels was reached.

The technique has been tried in a closed quarry, but it's believed to be the first time liquid potash has been used in open water. Scientists who study the mussels say the experiment in Manitoba is a "golden opportunity" to find a way to prevent their proliferation in water bodies around the world.

Rob Nedotiafko, who co-ordinated the treatment for Manitoba Conservation, says all the zebra mussels have been killed at Winnipeg Beach, where they were first found last October.

"It went really well," he said Monday, although Nedotiafko added there is no way to know exactly how many zebra mussels in the harbour were destroyed.

After the harbours were sealed off, live imported zebra mussels were lowered into the water in cages as a way of monitoring the experiment. When those mussels died, scientists knew the potash had been a success, Nedotiafko said.

"It's essentially a canary in a coal mine situation," he said. "The potash concentrations that were achieved had that desirable effect on the sample mussels, so the assumption is that everything else that was in there was also killed as well."

The province sealed off the harbours after the May long weekend and predicted they would be reopened by early June. The treatment is on schedule and the four targeted spots are expected to be free of zebra mussels in the next few weeks, Nedotiafko said.

Conservation Minister Gord Mackintosh said the province knew it had to act if there was to be a "fighting chance" of keeping the mussels out of Lake Winnipeg. The potash plan will cost $500,000, but Mackintosh said it could save millions down the road if the mussels are eradicated.

"This is a difficult situation and the implications can be long-term," he said in the legislature Monday. "Where we do have some information about the prevalence of zebra mussels, (they) are treated according to the best science that is available."

The province is focusing on a long-term strategy to ensure the mussels don't take hold, he said.

"We'll ensure that the surveillance is increased."

But Conservative critic Shannon Martin said even though the government has spent $500,000 dumping 400 tonnes of potash in the harbours, he hasn't heard a long-term strategy to ensure the mussels don't return once the curtains are raised.

The province owns only two decontamination machines which hose down boats when they come out of the water and are able to detach the mussels, he said.

"There doesn't seem to be a plan to do followup," he said.

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.

The mussels reproduce quickly and can disrupt the food chain, clog water pipes and create algae.