Zebra mussels haven't spread to any new Manitoba lakes this year — yet, officials say

The battle against zebra mussels is one with very few victories, but on the bright side officials say the prolific freshwater pest hasn't been established in any new Manitoba lakes or streams this year.

"Good news is as far we know they have not spread to any other water body," said Candace Parks, an aquatic and invasive species specialist with the province.

"People tell me all the time when they're on Lake Winnipeg, 'How do we get rid of this?' And I have to say to them, hopefully with a straight face, 'We can't.'"

Zebra mussels were first detected in Lake Winnipeg in 2013 and are now well-established in three Manitoba waterways. They were detected in the Red River and Cedar Lake in 2015, according to the Manitoba government.

In 2016, Singush Lake in Duck Mountain Provincial Park was effectively quarantined after zebra mussels turned up in a water sample. Day-use boaters, those most likely to spread invasive species from lake to lake, weren't allowed to launch boats on Singush this past summer.

So long as they don't remove and take their boats to other waterways, cottagers on the lake have been allowed to continue boating on the Singush, Parks said. "So I still say we only have three water bodies that are invaded with zebra mussels."

"We've essentially contained that lake and that lake is still under an investigation," she said.

By far the most noticeable impact the fingernail sized mussels continue to have is in the southern basin of Lake Winnipeg.

There were several reports and photos this past summer of mats of the sharp-shelled mollusks glued to docks, outcroppings of rocks and even on beaches in the area. Parks says that tends to happen after a major wind event, when aggressive waves force water levels up in the north basin, dislodging and laying bare mussels that are usually below the surface in the south.

Stemming the spread

One of the first attempts to stem the spread was in 2014, when the province dumped loads of liquid potash into four harbours on Lake Winnipeg hoping to snuff out the mussels.

The experiment killed most of the mussels at each site, Parks said, but they were found in the middle of the lake a short-time later.

"The potash treatment has never been done on a water body the size of Lake Winnipeg. Lake Winnipeg is the size of some countries, so it was unprecedented," she said. Parks didn't rule out the possibility that they will use potash again.

Parks and Alexis Kanu, executive director of the Lake Winnipeg Foundation, both agree that as far as the invasion in Lake Winnipeg and the threat of spread to other lakes goes, the best offence is a good defence.

"The sad news is we're not going to get them out of Lake Winnipeg, but there are so many other water bodies in Manitoba that we can protect from further invasion," said Kanu.

"I think we can't say it enough: humans are responsible for the spread of zebra mussels and the more that we know this and understand this and prevent the spread, the safer we'll keep our other lakes."

Parks said there's a simple but crucial three-point process boaters must follow if they're moving watercraft around different lakes and rivers.

After taking a boat from a lake, it's important boaters clean, drain and dry the boat from stern to bow, and that includes a thorough inspection of the hull, motor, trailer and areas that could carry stowaways. Any aquatic vegetation on the boat should be pulled off and chucked in the trash or destroyed.

Stowaways caught at U.S. border

Parks said she thinks Manitobans are starting to take zebra mussels more seriously, but it's clear the message needs to spread further before they do. 

On Sept. 6, Canadian Border Services Agency turned away a watercraft at the Emerson border port that had zebra mussels on it, Parks said.

The world-class fall walleye fishing season is upon us now, which Parks says attracts many U.S. anglers to Manitoba every year.

Parks said the province's watercraft inspection runs until October, but conservation officials had already inspected 8,000 boats as of Sept. 15, up from about 5,000 in 2006.

Foul algae

Zebra mussels eat algae, but they're not just insatiable opportunists that will eat up just any algae. They're selective filter feeders and may not develop a taste for the toxic blue-green algae that is causing problems in Lake Winnipeg.

Parks said zebra mussels might in some ways make the algal blooms worse on Lake Winnipeg in the long run. At the same time, the waters in some parts of the lake that have been gunked up with algal blooms in recent years appear to be clearing up, which Parks says could be attributed to the mussels changing eating habits.

"I don't know if it's going to get better before it might get worse," Parks said. 

"You can't get rid of them once they establish, so let's prevent it from happening in the first place, let's learn from Lake Winnipeg and not have this happen anywhere else."