Zebra mussels flex reach, threaten northern Lake Winnipeg and Manitoba Hydro stations

The zebra mussels that have invaded Lake Winnipeg might actually do some good for the southern side, but the north basin might not be so lucky — and that means impacts to the fishing industry and Manitoba Hydro, says a research scientist.

1 zebra mussel can produce a million eggs during single spawning season, says Lake Winnipeg Foundation

Zebra mussel shells piled up on Victoria Beach on the May long weekend. (Submitted)

The zebra mussels that have invaded Lake Winnipeg might actually do some good for the southern end of the lake, but the north basin might not be so lucky — and that means impacts to the fishing industry and Manitoba Hydro, says a research scientist.

Other than a frightful and potentially painful pile of sharp-edged shells washing up in the spring, beachgoers in the south basin of the lake might not even notice much of a change.

​"The concerns are all over the map about what's going to happen to the lake. We've heard everything from zebra mussels won't have a big impact on the lake to the lake is dead," said Scott Higgins, research scientist with the International Institute for Sustainable Development's Experimental Lakes Area, southeast of Kenora, Ont.

"I've seen the full range of comments on that. It's obvious there is some uncertainty there."

Scott Higgins says there's a lot of hard, rocky lake bottom in the northern basin of Lake Manitoba, where zebra mussels can colonize quickly. (Submitted by Scott Higgins)

The invasive species is a filter feeder, sifting large amounts of plankton and other microscopic detritus from the water and devouring that material.

"In many lakes they've shown to clear up particulates in the water, reduce the amount of algae and make water clarity higher," said Higgins, adding that each mussel can filter as much as one litre of water every day.

May reduce algal blooms

Multiply that by millions of mussels and that's a big impact.

"In some ways, it's a good thing. Maybe it will reduce algal blooms," Higgins said. "But there's always a concern when mussels are really effective at doing this because algae represents the base of the food web.

"If the base of the food web significantly declines, there is concern those effects may move up the food web to invertebrates, which also feed on that algae, and ultimately to the fish community, which feeds on those invertebrates."

In small or shallow lakes and rivers, that can be devastating to the entire ecosystem. In bodies of water like that, the mussels can filter the equivalent of the entire volume of water in the lake in just a couple of days, Higgins said.

"But in a really large lake, like Lake Winnipeg, that's simply not feasible, at least not in the south basin," he said.

That's because that part of the lake is filled with too much loose sediment to become overrun by mussels. That sediment gets stirred up in windstorms and the mussels don't like that, Higgins said.

Zebra mussel shells at Victoria Beach on May long weekend. (Submitted)

They grow attached to hard surfaces — rocks, docks, boats. They can also grow on aquatic plants and consolidated sediment, which is rock made from materials that have been cemented together like sandstone.

​"What this all means is they are likely to be restricted to the edges of the lake, where there are rocky shores and docks," he said.

So in beach areas, you may find a rock or some boulders and docks with zebra mussels but that's about it, aside from the spring piles.

Those are due to mussels dying off naturally, during winter, or from getting crushed by the thick ice. In spring all those shells get washed onto the beach, Higgins said.

"But I don't see any evidence so far that zebra mussels are going to colonize the middle of the southern basin to any great extent," he said.

And zebra mussels growing around the edge of the lake can't filter all the water in the middle of the lake.

"So, while there's still a lot of uncertainty about the magnitude of impacts in Lake Winnipeg, I suspect they're going to be smaller than we've seen in some other ecosystems," Higgns said.

Manitoba Hydro employees monitor for zebra mussels at the Seven Sisters Generating Station on the Winnipeg River. The mussels have not yet been detected in the Winnipeg River system. (Manitoba Hydro)

It also means they may take care of some algal blooms in the lake but they're not exactly going to make it crystal clear — there's too much water for that.

"And the growth rates of the algae are … much higher than zebra mussels' ability to consume them. That's what the evidence suggests so far," Higgins said.

1 mussel, 1 million eggs

But through the narrows and into the northern basin of the lake there's a lot of hard, rocky lake bottom where zebra mussels can colonize, he said.

Once they can do that, they do it fast.

One mussel can produce up to one million eggs during a single spawning season, according to the Lake Winnipeg Foundation. And they are dense, with more than 10,000 mussels per square meter in some places.

They also grow on the shells of native mussels, clogging their intake filters and choking them out. 

"There is a rule of thumb that basically says that, within 10 years of a zebra mussel invasion, you lose about 90 per cent of your native mussel population," Higgins said.

Now back to that filter-feeding that they do.

If they can spread out to the middle of the northern basin and blanket that rocky bottom, they could remove a lot of the sustenance from the food chain.

"It's possible that as the water moves from the southern basin through the narrows and into the northern basin, the zebra mussels may be able to strip out the algae and the nutrients they contain," Higgins said.

"This is all speculative and we don't have any data yet, but it's something we're watching to make sure we catch this if it starts to happen."

Zebra mussel larvae have already been found near Matheson Island, the southernmost point shown on this map, and as far north as George Island. Manitoba Hydro is in the midst of a plan to install a treatment system to deal with mussels at its Grand Rapids and Jenpeg generating stations, also shown on this map. (Google Maps)

Recent data from the province shows zebra mussel larvae — called veligers — are moving north and have already been found near Matheson Island, at the south end of Lake Winnipeg's north basin, and as far north as George Island, more than 300 kilometres north of Winnipeg.

Hydro monitoring for mussels

Manitoba Hydro is in the midst of a plan to install a treatment system at its Grand Rapids Generating Station, as well as at the Jenpeg Generating Station on the upper arm of the Nelson River.

"As the invasive zebra mussels spread, they pose a threat to pipes, pumps and other equipment at Manitoba Hydro's generating stations," said spokesman Bruce Owen.

"[They] can attach to the inside surfaces of a generating station's intake pipes, plugging them up. These pipes supply water to cool turbines to prevent overheating and for emergency fire suppression."

The Grand Rapids Generating Station, which sits on the Saskatchewan River between Cedar Lake and Lake Winnipeg. (Manitoba Hydro)

The plan is to use chlorine in the water system used to cool the generators, while the fire protection system will be protected by using a potassium chloride treatment.

"However, I caution that this is simply a plan. Any potential treatment for zebra mussels is subject to federal and provincial regulatory approval," Owen said.

If approved, generating stations further downstream will be outfitted a little later, Owen said.

The first detection of zebra mussels on Hydro infrastructure was at the Selkirk generating station in October 2015. The mussels had attached themselves to a water intake screen.

"The same year saw a single tiny zebra mussel larva [also known as a veliger] detected in Cedar Lake, upstream of the Grand Rapids generating station. Ongoing testing to date has found no adult zebra mussels in Cedar Lake," Owen said.

For the first time, this year Hydro is conducting a veliger sampling program, he added, noting the only sampling until now has been for adult mussels.

Hydro employees will sample the following water bodies twice during 2018:

  • Cedar Lake.
  • Playgreen Lake.
  • Nelson River upstream of the Kelsey and Kettle Generating Stations.
  • Assiniboine River near Brandon generating station.
  • Winnipeg River upstream and downstream of the Pointe du Bois and McArthur Falls generating stations.


Frequently asked questions on mussels

  • What are they and how did they get here?

Zebra mussels are an aquatic invasive species, which means they are not native to this region and can multiply rapidly.

They are native to the Black and Caspian sea region of eastern Europe and are believed to have been carried to Canada's Great Lakes by big ships.

They were first discovered in Lake Erie in 1986 and within a few years, they had spread to the rest of the Great Lakes.

After a decade, they were in all the Great Lakes as well as smaller inland lakes and rivers, and had spread as far south as the Gulf of Mexico. They now occupy over 800 lakes, mostly in eastern North America, according to Higgins.

  • How did they arrive in Manitoba?

They were first found in Manitoba in Lake Winnipeg in October 2013.

Evidence suggests that they came in via the Red River, either in the form of a veliger or as adults floating down the river, attached to debris or plant material, Higgins said.

Zebra mussels coat a boat's stainless steel trim tab and cylinder in Gimli in this 2015 file photo. It's been suggested zebra mussels arrived in Manitoba attached to a boat or other equipment being transported from an invaded habitat. (Submitted by Dean Thorkelsson)

It is also possible that they arrived overland attached to a boat or other equipment being transported from an invaded habitat. The closest invaded habitats are in North Dakota and Minnesota.

  • Are there health concerns?

There are none immediately known, other than cuts from the sharp-edged shells.

Around rocky shorelines, caution needs to be taken so that people, especially children, and pets aren't cut by the sharp shells. That means wearing proper footwear in the water. 

In the Laurentian Great Lakes, it has been reported that mussels helped develop shoreline algal blooms from their waste products — feces and urine. As those blooms washed up on the beaches, they became a cesspool for bacteria, Higgins said.

An algae bloom covers Lake Erie near the City of Toledo water intake crib in this August 2014 file photo. (Haraz N. Ghanbari/Associated Press)

There are scientific papers about the beaches on Lake Michigan that suggest decaying material was associated with a number of potentially pathogenic bacteria — E. coli and others that could pose a concern to human health.

So whenever officials saw these shoreline algal blooms washing in and staring to decay, they would essentially have to close the beach.

  • What kills them?

That's what everyone wants to find out.

The province tried suffocating them with liquid potash in May 2014, and temporarily closed four harbours where zebra mussels had been found.

That killed some in Winnipeg Beach, Gimli, Arnes and Balsam Bay, but those areas have since been re-invaded. For big bodies of water, the potash gets too diluted.

Ice buildup on the lakes will crush the mussels, forcing the dead shells to wash up in spring. Some mussels, however, survive in crevices in rocks, then repopulate quickly in the spring when the ice is gone, Higgins said.

"So ice in itself won't kill off the population, unfortunately. They just keep rebounding every year."

  • What can the public do?

The most important action that individuals can take is to ensure that they thoroughly clean items (like boats, boat trailers and buoys) removed from Lake Winnipeg before placing them in another water body, Higgins said.

As well, boat hulls, motors, water intakes and other "in-lake" infrastructure will likely require increased maintenance.

About the Author

Darren Bernhardt


Darren Bernhardt spent the first dozen years of his journalism career in newspapers, first at the Regina Leader-Post then the Saskatoon StarPhoenix. He has been with CBC Manitoba since 2009 and specializes in offbeat and local history stories and features. Story idea? Email: