Zebra mussels are freshwater hinged mollusks. They are filter feeders that attach themselves to solid surfaces. They breed very quickly, as females can release up to one million eggs each breeding season. After the eggs are fertilized, larvae (called veligers) emerge and are free-floating for up to a month. The larvae are microscopic and do not swim. Veligers float through lake and river currents until they settle on a solid surface. This natural dispersal method means they can easily affect waterways downstream from an invaded area. Zebra mussels have few, if any, natural predators in North America. As a result, they often permanently alter the food web and ecosystems they invade.

Zebra Mussels can have significant negative impacts on people, such as:

·  Increased maintenance costs

·  Damage to equipment such as boats, hydro-electric generating facilities, water intakes and other infrastructure along infested water bodies

·  Injury from sharp shells

·  Potential negative health impacts resulting from increased likelihood of toxic algae blooms

·  Beach closures

They also have negative effects for freshwater habitats, such as:

·  Altering the food web by out-competing native species, like native mussels and other small invertebrates, for food (plankton).

·  Removing large amounts of non-toxic algae (plankton) from the water and leaving behind toxic algae (cyanobacteria) to thrive, causing toxic algae blooms

·  Affecting fish spawning areas by changing the surfaces of rocks and vegetation, impacting the survival of fish eggs

·  Creating clearer water, allowing sunlight to penetrate deeper and changing the habitat by increasing the growth of submerged aquatic vegetation.

Zebra mussels are especially harmful to native mussels, many of which are species at risk. They outcompete these species for food and will attach themselves to native mussels, suffocating them.

An infestation of zebra mussels in Clear Lake presents a real threat of significant and irreversible damage to the lake and downstream waterbodies.

Discovery of Zebra Mussels in Clear Lake
Clear Lake is a unique lake for the prairie parkland area. It is oligotrophic, meaning it has low amounts of nutrients in the lake, giving it a clear look and making it a suitable source of clean, fresh drinking water. Clear Lake is key habitat for 14 fish species, including whitefish, northern pike, white sucker, walleye, and slimy sculpin. Whitefish are the most abundant large-bodied fish in Clear Lake and are usually found in the deeper parts of the lake along with slimy sculpin. Both species are considered ecological indicators of the health of the lake as they require a well-oxygenated lake bottom to survive.

In November 2023, Parks Canada officials removed a clump of live zebra mussels from Clear Lake in Riding Mountain National Park. This prompted the search for further evidence of their presence somewhere in Clear Lake. Over the winter, water samples were collected from Clear Lake and tested for zebra mussel environmental DNA (eDNA) at the Freshwater Institute operated by Fisheries and Oceans Canada in Winnipeg.  In cold water, zebra mussels are less metabolically active and are much less likely to shed eDNA; therefore, zebra mussels may be present despite the negative eDNA results from this winter. Positive eDNA samples can give a better idea of where a population might be located. Sampling continued until the ice was no longer safe and will resume on open water as soon as possible.

Parks Canada staff at Riding Mountain National Park are working with AIS specialists from other Parks Canada administered sites, Members of Keeseekoowenin Ojibway First Nation, the Province of Manitoba’s AIS Unit, and Fisheries and Oceans Canada. The Keeseekoowenin Ojibway First Nation (KOFN) maintains authority and control of fishing station IR 61A on the northwest shores of Clear Lake.

The likelihood of success for any potential eradication action will depend on whether an intervention can happen before significant reproduction and spreading occurs within the lake. Determining with relatively high confidence where they exist in the lake would help to inform potential eradication options.

Timeline

Summer 2011 – Monitoring for zebra mussels in Clear Lake begins.