Fighting the zebra mussel: tiny clam-like creature has calamitous potential to damage fisheries, water systems

Last Updated by Kevin Woster on
Expect to see more inspectors like Ryan Rabern, seen here at Angostura

Twenty years ago, I saw my first zebra mussel.

It was not a pretty sight, at least not for anyone who understood the proven potential for environmental damage from infestations of the tiny freshwater clams. Most are only about the size of a lima bean, but they are nonetheless an invasive species with explosive reproductive capabilities harmful impacts on natural aquatic systems and the native species they support.

To say nothing of the effects on expensive water systems and energy facilities. 

Zebra mussels surfaced in the flow of South Dakota news last month after they were confirmed in Lake Sharpe, one of the four popular Missouri River reservoirs in South Dakota. That led the state Game, Fish & Parks Department to post warning signs noting the infestation and increase monitoring at boat ramps on Sharpe, as well as issue news releases warning boaters to take care not to contribute to the spread of the mussels.

It also inspired Gov. Kristi Noem to make a public service announcement, which was released to reporters on Tuesday. It’s an important PSA that should be required watching for anyone who moves a watercraft from one lake, stream or river to another these days.

Because if you’re a boater or jet-ski operator and you’re not careful, invasive species including the zebra mussel, could be moving with you from one invested body of water to one that hasn’t yet been infested. And you could be the one to spread the infestation.

Don’t be that one. Listen up. Pay attention. Heed the warnings. Learn about the mussel and its threats and figure out what you need to do with your boat and jet ski and your minnow buckets to stop the spread of aquatic invasive species.

The discovery of zebra mussels in Lake Sharpe was a surprise, and an unpleasant one. But it wasn’t the shock brought by the discovery in the spring of 1999 of zebra mussel on the water intake of a MidAmerican Energy Co. power plant on the Missouri River south of Sioux City, Iowa.

Not long after that discovery by MidAmerican Energy employees Bill Johnson and Steve Lambing as they were cleaning intake equipment, I traveled to Sergeant Bluff, Iowa to see the location of the first confirmed zebra mussel in the Missouri River.

There with Johnson looking on, Lambing held up a small bottle of water with a tiny clam drifting around inside. It didn’t look like much, but it was.

The mussels, which are native to eastern Europe and likely were released in the Great Lakes from ocean-going ships. had previously been confirmed in a variety of locations in the Mississippi River before the find at Sergeant Bluff. But that was the first in the Missouri. A federal invasive species specialist I interviewed said at the time that the Missouri River had kind of been considered a “line in the sand” that biologists hoped the zebra mussel wouldn’t cross.

That line has long since disappeared as a perhaps delusional demarcation of hope.  And it was a surprise to invasive-species specialists that the first zebra mussel confirmation in the Missouri came so far upriver from its joining with the Mississippi.

Since then, the spread has continued, as expected. Zebra mussels have been confirmed in the Missouri River below Gavins Point Dam in Yankton, and above the dam in Lewis and Clark Lake. That confirmation came in the fall of 2014, and it was a single adult zebra mussel.

Then in 2015, a reproducing population was documented in the reservoir.

“In Lewis and Clark, they’re very dense in places,” says John Lott, aquatic resources chief for the Game, Fish & Parks Department in Pierre. “In Sharpe we’ve only seen small clusters, in the places that have seen the most sampling. The Corps of Engineers initially noticed mussels at the dam, while doing maintenance.”

More sampling by GF&P and the U.S. Fish and Wildlife Service confirmed zebra mussels at other locations in the lower part of the reservoir. Presumably they will work their way up the reservoir. But boaters failing to take proper precautiouns when they leave the lower portions of the Sharpe could spread them faster to the upper portion in the Pierre area, Lott said.

“On their own, zebra mussels will work their way upstream in a reservoir slowly,” Lott adds. “But the flows we have in Lake Sharp, especially at the upper end, would slow down that movement. But when you start thinking about watercraft, that’s where these buggers are going to be hitching a ride.”

So far, they haven’t been confirmed in Lake Francis Case, the reservoir backed up by Fort Randall Dam upstream from Lewis and Clark and downstream from Lake Sharpe. Nor have they been confirmed in Lake Oahe, the largest of the four Missouri River reservoirs in South Dakota.

Yet. It seems unlikely that Francis Case has escaped the mussels, since they are in reservoirs above and below and boat traffic from other areas is heavy on the reservoir.

“My bet is we’ve got them in (Francis) Case,” Lott said.

Continued surveys this fall and next spring will help determine that. And Oahe?

“That’s a tough one,” Lott said. “We are at the early stages with the Sharpe infestation this year, but there’s a lot of boat traffic from Sharpe, day to day.”

It’s common for anglers to fish Lake Sharpe below Oahe Dam one day, such as when it’s windy and the bigger lake is more difficult to handle, then fish above the dam the next day if things have settled down.’

Plus, boats form other states, including those in the Mississippi drainage, are common arrivals at Oahe Ramps.

“It’s going to be a challenge. And we’ll certainly work on a plan to stop it from happening on Oahe,” Lott said. “But there are no guarantees.”

Lott said Governor Noem is fully committed to fighting the spread of the invasive species, and that fight is likely to involve a multi-agency approach.

“One thing our (GF&P) commission and the governor have been visiting about is making AIS (aquatic invasive species) management more of a combined state-government response, rather than just GF&P,” Lott said. “We’ve already met with other agencies and we’re trying to identify how other agencies can help with AIS management and enforcement.”

It’s an issue likely to show up before the GF&P Commission and probably in the state Legislature.

“One thing that’s being talked about is pursuing a more mandatory approach to boat inspections and decontaminations,” Lott said.

Staffing levels will be part of that discussion, too, Lott said.

“To have more staffing you need to have something for staff to do, and you need the resources to have them out there doing it,” he said. “So potentially you’re talking money, equipment and maybe additional authority.”

More money, more staffing, more regulations is not a legislative trifecta that commonly wins support in the generally conservative South Dakota. But the zebra mussel and its continued comes with a price tag that’s hard to calculate.

They can attack to just about any hard surface, from submerged rocks to water pipes to boat motors to native clams -- sometimes suffocating them. They can filter out essential nutrients in water systems that affects the quality and sustainability of the entire food chain. And they can complicate and add to the costs of running a water system that feeds from an invested water body.

“People think it’s about fish and being able to catch fish,” Lott said. “But the biggest impacts have been on the water-infrastructure systems. They impact those systems in what they have to be operated differently or constructed differently, and those costs end up being passed on to the water users.”

Which leaves plenty to talk about between now and next year’s boating season.

The views expressed here are those of the author and do not necessarily represent or reflect the views of SDPB, Friends of South Dakota Public Broadcasting, or the State of South Dakota.