Zebra mussels, an invasive species that provincial conservation officials have been concerned would show up here, have been found in Lake Winnipeg.
The province said the freshwater molluscs that can multiply rapidly were recently found on the hull of a private boat and a dock at Winnipeg Beach, and on some fishing boats dry docked at Gimli.
Manitoba Conservation biologist Laureen Janusz said it's a mystery how they got there.
"We're not quite sure exactly how they arrived in Lake Winnipeg," she said. "There are a couple of options: either dispersed through the Red River - they have been found in North Dakota - or through an infested watercraft or equipment."
Janusz said the province is acting quickly to determine the extent of the infestation.
"We're really concerned and would like to minimize the potential to spread zebra mussels to a lot of our inland waters and lakes."
She said the species poses a threat to boats, docks and can clog water treatment plant intake and discharge pipes, encrust in-water infrastructure, foul boat motors and may affect beaches.
Ontario, Minnesota and North Dakota have established populations of zebra mussels.
Provincial officials said staff are on site at Winnipeg Beach, Gimli and Hecla to provide information to watercraft owners and local residents to help identify zebra mussels and collect samples, and provide advice on how to prevent further spread.
They said watercraft inspection teams will be in the Winnipeg Beach and Gimli areas from this weekend until lake freeze-up.
The public can call 1-877-867-2470 (toll-free) or go to the province's website for more information.