WINNIPEG - Zebra mussels are spreading in Manitoba despite a unique experiment intended to stave off an invasion of the shellfish.
Manitoba Conservation says the mussels have been discovered in at least six spots on Lake Winnipeg.
They have also turned up again in the four harbours that were treated with potash this spring to kill them.
Department staff say the mussels are reproducing outside the treated harbours and moving back in.
The province says it's stepping up monitoring efforts and will train a canine unit to sniff out the mussels on watercraft.
It has also set up decontamination units at high-traffic harbours such as Gimli, Winnipeg Beach and Selkirk Park.
The province had declared victory over zebra mussels in June after it doused the four infested harbours with liquid potash. The areas were sealed off and the potash injected into the water to eventually suffocating the mussels.
The harbours were initially declared free of the mussels, but that changed earlier this month.
The invasive species, which has been in the Great Lakes for almost two decades and has spread throughout parts of the United States, was discovered for the first time in Manitoba last October.
The mussels reproduce quickly and can disrupt the food chain, clog water pipes and create algae.