Lake Sharpe has become the second major Missouri River reservoir in South Dakota to be infested with invasive zebra mussels, raising fears that millions of dollars in mitigation may be needed and that new restrictions could be placed on those who use the lake for boating, fishing and recreation.
The infestation was announced in a news release from the state Game, Fish & Parks Department on July 12. The mussel discovery shocked state GFP officials and came in spite of more than four years of work and $400,000 in spending aimed at preventing boaters from inadvertently spreading zebra mussels and a host of other harmful, non-native species from spreading further into South Dakota.
On July 13, GFP Chief of Aquatic Resources John Lott told South Dakota News Watch that senior GFP staff plan to meet soon to begin reevaluating how the state handles aquatic invasive species management.
South Dakota faces staggering mitigation and repair bills as a result of zebra mussel infestations. Little can be done to reverse the infestation in Lake Sharpe, which is located on the Missouri River between Pierre and Fort Thompson. There is no known way to completely remove zebra mussels from a lake without either draining it or using poison to eradicate the mussels, which is not an option for a river-based waterway.
“We’ll be recommending regulation changes at the [GFP] commission meeting in September,” Lott said, though he did not provide any specific potential rule changes.
For now, the rules have not changed for boaters using Lake Sharpe, Lott said. Still, he wanted to remind the public that the only way for mussels to move from lake to lake is if people accidentally carry them in or on their boats.
Zebra mussels, native to Eastern Europe, have been the bane of waterway managers and users across the country.
South Dakota already faces steep mitigation and repair bills on public waterways and related infrastructure as a result of ongoing zebra mussel infestations, including at Lewis and Clark Lake on the Missouri River near Yankton.
The mussels can clog or damage water treatment and power-generation systems on lakes and rivers. When the mussels have been in a water body long enough, the sharp shells of dead mussels start to accumulate on beaches, fouling recreation access points and potentially cutting the feet of users. When water levels are drawn down, massive mussel die-offs release strong odors. The mussels can darken lake waters and make fishing more difficult. So far, zebra mussel infestations haven’t been found to destroy fisheries, but the potential does exist, Lott said.
Mussel mitigation a costly process
A January 2019 report by the University of Montana gave a glimpse of what an expanded zebra mussel infestation could cost South Dakota.
A study done at the university’s Flathead Lake Biological Station estimated the potential yearly cost of zebra mussel infestation solely to irrigation systems along Montana’s portion of the Missouri River at $25 million to $53 million. The potential cost of mussel removal and mitigation at water treatment plants was estimated at up to $5.8 million, the study found. A similar report does not exist for South Dakota but many farmers, ranchers, cities and rural water systems draw water from the state’s portion of the Missouri River. Costs to the state and potentially to private landowners increase if mussels spread to new lakes and rivers.
Zebra mussels cause damage by attaching themselves to nearly any hard surface in the water. Juvenile zebra mussels, which are known as veligers, are nearly microscopic and float free in the water for about a month. During that month they can be sucked into boat ballast tanks, live wells and motors, which is how they move from lake to lake. Not only does that allow zebra mussels to spread easily, it also means they can get into some pretty surprising places. Zebra mussels also tend to form colonies which can clog intake and outflow pipes at water treatment facilities.
Lewis and Clark Lake, the first Missouri River reservoir in South Dakota where a zebra mussel infestation was found, has suffered extensive damage and hefty repair bills. At Gavins Point Dam, which forms the reservoir, the U.S. Army Corps of Engineers had to reduce the amount of electricity the hydroelectric dam produces in order to clean mussels out of generator cooling tank water intakes every two weeks, officials said. Prior to the zebra mussel invasion, the intakes were cleaned about every six months.
“They’ll attach to piping. If it’s really small piping they’ll completely block it up, stop the flow through it. They reduce the amount of flow through the system, they can completely block the heat exchangers or reduce the flows, which of course starts to make our unit temperatures creep up, forcing us to shut a generator down to clean it out,” Gavins Point Dam senior mechanic Michael Schnetzer said in a June news release announcing a new anti-mussel water filtration system.
The filtration system the corps announced in June cost about $1.45 million and works by bombarding free-floating juvenile zebra mussels with a powerful UV light, which kills them.
The first discovery of zebra mussels in the U.S. was made in 1988 in the Great Lakes. Within a few years, nearly every submerged surface in the Great Lakes was covered in the mussels. Since being discovered in the U.S., zebra mussels have spread outward through the country by way of river currents and in boat ballast tanks, live wells and motors.
The first confirmed discovery of zebra mussels in South Dakota occurred in 2015 at Lewis and Clark Lake on the Missouri River near Yankton. They have since been found in Lake Yankton, which is just outside of Yankton, in McCook Lake in Union County near North Sioux City and in the Missouri River below Gavin’s Point Dam. Lake Sharpe is the newest addition to the list of infested South Dakota waters.
GFP Commission Chairman Gary Jensen said he is concerned about the potential for damage and repair costs to Lake Sharpe and is working to schedule an emergency commission meeting to form a response.
His goal for the meeting was to get a more detailed report on the Lake Sharpe situation and determine what, if any, mitigation steps can be taken.
“We’ve been trying to prevent this from happening since I started on the commission,” said Jensen, a commissioner for about a decade.
The first adult zebra mussels found in Lake Sharpe were discovered recently by U.S. Army Corps of Engineers staff members doing maintenance on Big Bend Dam, which forms the lake at Fort Thompson. It is impossible to know exactly how the mussels got there, but the most likely scenario is that juvenile zebra mussels were carried into the lake by a boater.
So far, adult mussels have only been found on structures close to the dam. GFP staff will be working to determine the full extent of the infestation in the coming days, Lott said. They will also monitor Lake Francis Case, which is immediately downstream of Lake Sharpe, for signs of zebra mussel infestation. Lake Oahe, which is immediately upstream of Lake Sharpe, also will see more monitoring for mussels, Lott said.
Little can be done to immediately reverse the infestation in Lake Sharpe since there is no known way to completely remove zebra mussels from a lake without either draining it or using poison to eradicate the mussels, which is not an option for a river-based waterway.
However, the GFP commission can strengthen state anti-aquatic invasive species rules and step up enforcement among boaters and recreational users to prevent or slow the further spread of zebra mussels. The commission also could declare Lake Sharpe an invasive species containment water, a designation that carries a set of additional significant restrictions on boat movement and cleanliness.
“There are still a lot of water bodies out there to be protected,” Jensen said.
New boating rules and enforcement likely
The state’s current invasive species rules first were written in 2015 following the discovery of zebra mussels in Lewis and Clark Lake. The rules were updated again in 2017. Boat owners are required to pull their boats’ drain plugs before leaving a boat ramp parking lot. Boaters and anglers also are not allowed to transport lake water past a boat ramp parking lot. Any boat launched into a lake or river designated by the GFP Commission as an invasive species containment water and that can’t be completely dried out by pulling a drain plug must be decontaminated by cleaning the boat’s hull with 140-degree water and flushing its internal compartments with 120-degree water.
Right now, there are four invasive species containment waters in South Dakota, making up the only waterways other than Lake Sharpe where zebra mussels have been found in the state. The containment waters are Lewis and Clark Lake, the Missouri River below Gavins Point Dam, Lake Yankton and McCook Lake near North Sioux City.
Any boat that has been used on an out of state lake or river known to have invasive mussels also must be decontaminated before it can be launched in South Dakota. GFP staff can inspect boats for compliance with the rules but, so far, most enforcement efforts have been focused around Lewis and Clark Lake.
Jensen wouldn’t say whether he thought the state’s current approach toward invasive species control had been aggressive enough.
He also couldn’t offer any details on changes that might be in the works but he did say that he wanted to move as quickly as possible. Any rule changes the commission chooses to make would be subject to a 30-day public comment period and a public hearing.
"Now that they’re here, we’ve got a real problem.” -- Fort Pierre boater Rick Jorgensen
Rick Jorgensen, a boater from Fort Pierre who spent a recent afternoon cruising up and down Lake Sharpe with friends, wasn’t happy to hear about the zebra mussel infestation.
“Now that they’re here we’ve got a real problem,” Jorgensen said.
He said he was frustrated at the inability of state officials to keep a closer eye on all the boats coming into South Dakota from Minnesota and Iowa where there are dozens of lakes infested with zebra mussels.
“I don’t think GFP has enough people to do anything about it,” Jorgensen said.
At least part of the urgency from GFP officials has to do with the popularity of Lake Sharpe and its downstream neighbor, Lake Francis Case. Lake Francis Case likely will be infested with zebra mussels soon, if it isn’t already, because juvenile zebra mussels will be sucked through Big Bend Dam. Lake Francis Case is crossed by Interstate 90, making it an easy destination for anglers and boaters from Rapid City or Sioux Falls to make weekend visits.
“When you look at a state like ours and how mobile our boaters and anglers are, it can be really hard to control the spread of aquatic invasive species,” Lott said.
A big part of GFP’s job over the next few months will be to convince boaters, anglers, cities and irrigators to start working together on efforts to prevent zebra mussels from spreading any further. The only way the invasive mussels can move past a dam or to another lake is if someone inadvertently carries them, Lott said.
“We need to get people to think about how aquatic invasive species impact them directly,” Lott said.
Paul Lepisto, an angler and boat owner from Pierre, said the discovery of zebra mussels was a “gut punch.” Lepisto, who is the regional conservation director for the Izaak Walton League, has been working on the invasive species issue for 11 years. He said he thought GFP’s approach to the issue had been sensible.
“I thought the message would have sunk in; we can’t recreate the way we used to,” Lepisto said.
Rapid reproduction and vast movement
Zebra mussels are actually native to the Caspian Sea region of eastern Europe.
The mussels spread through Europe’s growing canal system during the 1800s and 1900s. Eventually they made their way to busy, freshwater ports that often saw ocean-going ships. Those ships picked up juvenile zebra mussels, which are known as veligers, as they pumped water into their ballast tanks before making their way across the Atlantic Ocean.
A few of those ships went through the St. Lawrence Seaway system, which connects the Atlantic Ocean to the Great Lakes. At some point along their journey through the Great Lakes, transatlantic ships carrying zebra mussels dumped their ballast tanks and almost immediately, the Great Lakes became infested.
Zebra mussels are small, filter feeding mussels that latch onto hard surfaces in infested lakes.
They grow fast and reproduce by broadcasting reproductive cells into the water. A single female can release up to 40,000 eggs during a spawning cycle and up to 1 million eggs during a summer spawning season.
Juvenile zebra mussels are nearly microscopic and float free in the water for about a month. They can be sucked into boat ballast tanks, live wells and motors. After about three weeks in the water, the veligers find something to latch onto, grow a shell and enter their adult stage of life. Zebra mussel colonies have been found on everything from golf balls to live turtles. Once attached to something, it takes a female about two years to start reproducing.
Zebra mussels feed by filtering water and collecting algae in their siphons. Algae are the base of most aquatic food webs, so there’s some worry that zebra mussels, which have few natural predators in North America, can cause irreparable harm to fisheries. While scientists worry zebra mussels can compete with native species that rely on algae, and thus alter food webs, it hasn’t happened yet.
The mussels can and do alter water clarity which can encourage the growth of aquatic plants and make fishing more difficult.
By far, the biggest danger zebra mussels pose is to infrastructure. National estimates peg the annual cost of mitigation, repairs and education about invasive mussels at about $1 billion.