Quagga mussels

Quagga mussels are shown in a sediment sample from Lake Michigan taken during a whole-lake benthic survey in June 2005.

Courtesy NOAA Great Lakes Enviro

HAMILTON – In the middle of March, officials in California sent a message to states north warning about a pontoon boat from Montana that was potentially packing an insidious cargo.

The boat had spent some time in Lake Havasu, where invasive quagga mussels are known to lurk.

Montana Fish, Wildlife and Parks aquatic invasive species specialist Linnaea Schroeer said the message indicated the boat had gone to one of California’s boat check stations and wasn’t decontaminated.

“In fact, the boat was allowed to enter California,” she said. “They have extremely strict protocols on addressing zebra and quagga mussels. Since we were the final destination, we were sent a notification.”

As were all the Western states on the designated route of the boat headed north.

The warning came thanks to an interstate compact called “Building Consensus in the West” that’s helping stop the spread of the tiny invaders that have the potential to create widespread ecological harm.

In their mature form, quagga mussels grow to about the size of a fingertip. Juvenile mussels are nearer the size of a Rice Krispy. And before they form a shell, their free-swimming larvae can’t be seen with the naked eye.

Introduced into the Great Lakes through the ballast of eastern European ships in the 1980s, zebra and quagga mussels have spread to many regions in the country.

Once an infestation occurs, the mussels can create massive colonies that consume large amounts of the microscopic plants and animals that form the base of a waterway’s food chain. Their waste can cause toxic algae blooms. And when they die, their shells can wash up on shore and create even more havoc.

“Their shells are very sharp and they can cut your feet,” Schroeer said. “Beaches all over the Midwest have been closed due to zebra mussels.”

If the mussels get a foothold in a person’s boat, they can colonize inside a motor or other internal system and ruin it. Domestic water treatment facilities have also been impacted.

So far, five Western states have been able to hold the line and keep the invasive mussels from gaining a foothold.

“We prefer to say undetected,” Schroeer said. “There’s often a lag time of two to three years before we can detect them in a water body. At low levels, it’s sort of like looking for a needle in a haystack.”

With the slim chance that some water body already holds a small population of the invasive mussels, it’s important that people hauling boats around this summer take the time to stop at any check station they pass inside Montana.

Since the larval stage can’t be seen with the naked eye, it’s also important that people drain their boats before moving them from one waterway to another.

“As far as we know, we don’t have quagga or zebra mussels in the state,” she said. “They have not been detected in Montana, Wyoming, Idaho, Washington or Oregon. We are sort of the geographic block in the West without a detected population. We want to keep it that way.”

That’s what makes the interstate compact so important.


The most recent case involving the boat traveling between Lake Havasu and Montana was a great example of how that cooperative effort is paying dividends.

The boat was checked as it entered Idaho and was found to be carrying quagga mussels, she said. The initial boat check site didn’t have decontamination equipment. The boat was moved to Salmon, where it was treated and released back to its Ravalli County owners.

“They were extremely cooperative,” Schroeer said.

Over the past two years of the interstate effort, there have been a number of occasions where different states, including Montana, were notified about the potential of boat carrying the invasive species.

“Luckily, in all the cases that we’ve dealt with, the owners have been very cooperative and easy to work with,” she said. “There is no cost to the boat owner to get a boat cleaned. As long as they are cooperative, there is no citation.

“It’s really in everyone’s best interest,” Schroeer said. “We really want to work with people and make the process as simple and without any to the boat’s owner. We just want to make sure it’s clean.”

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