State officials scramble to respond after zebra mussels found in Lake Sharpe

Reservoir is second on Missouri River to be infected

A pair of South Dakota conservation officers inspect Pierre resident Jeff Carr’s boat July 14 as part of a temporary law enforcement check station near Oahe Dam a few miles north of Pierre. Carr had been fishing on Lake Oahe and officers checked to make sure the boat’s drain plug was out, which is required under the state’s aquatic invasive species rules. Regional Conservation Officer Supervisor Steve Rossow said enforcement of the rules has taken on new urgency as Lake Sharpe was confirmed to be infested with invasive zebra mussels on July 12. (Nick Lowrey / South Dakota News Watch)

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 GF&P 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, GF&P Chief of Aquatic Resources John Lott said senior GF&P 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 and created by the Big Bend Dam. 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 [GF&P] 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

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 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.

Gavins Point Dam senior mechanic Michael Schnetzer said in a June news release that a new filtration system 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.


The first confirmed discovery of zebra mussels in South Dakota occurred in 2015 at Lewis and Clark Lake near Yankton. They have since been found in Lake Yankton, in McCook Lake in Union County and in the Missouri River below Gavins Point Dam.

GF&P Commission Chairman Gary Jensen said he is concerned about the potential for damage and repair costs to Lake Sharpe.

“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. 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.

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 GF&P 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.

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.

Jensen said he wanted to move as quickly as possible on any rule changes, which would be subject to a 30-day public comment period and a public hearing.

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.

Zebra, image of invasive mussels.jpg
Zebra mussels are generally small and can be identified by the distinctive stripes on their shells. If not contained, zebra mussels reproduce quickly and can damage waterways and boats and clog water treatment facilities and power plants. (U.S. Geological Survey photo)

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