Invasive zebra mussels confirmed at Smithville Lake

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Kansas City
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SMITHVILLE, Mo. -- Biologists on Wednesday determined that zebra mussels are present in Smithville Lake, a 7,200-acre impoundment north of Kansas City. Zebra mussels, mollusks which look like small clams, are an invasive species from Eurasia that can cause ecological and property damage.

Three zebra mussel shells were found on metal gates used to control water flow through the lake dam, said Mike Watkins, a wildlife biologist for the U.S. Army Corps of Engineers. The gates were inspected by Watkins and Eric Dennis, a fishery biologist for the Missouri Department of Conservation (MDC). They later also found a zebra mussel shell attached to a courtesy dock at the boat launch ramp near the Camp Branch Marina.

The mussels found at the dam were not alive because the gates were pulled from the water several days ago, Watkins said. But they had tissue inside the shells indicating that they were alive until recently. Because the shells vary in size, the mussels’ ages varied and that indicates that the lake has a reproducing population of zebra mussels, he said. The largest mussel was at least a year old.

How this will affect the sport fisheries and property at Smithville Lake is uncertain, said Tim Banek, MDC invasive species coordinator. It will take years of monitoring to gather data, and populations could rise and fall naturally.

“We really don’t know for sure what effect they will have in Missouri,” Banek said. “It could vary from lake to lake.”

Zebra mussels have caused billions of dollars in damage in the Great Lakes and Mississippi River systems. They filter plankton from the water, and because they can form large colonies, this can alter ecosystems and rob native fisheries of nutrients. The mussels attach to hard objects such as rocks, metal, boat hulls and water pipes. They also attach to each other, forming dense colonies that can clog pipes. Their sharp shells are a hazard to bare-footed swimmers, and the shells can cut fishing line when a fish hooked by an angler swims past a colony.

A female zebra mussel can produce more than a million eggs during the spawning season. The eggs hatch into a larval form, called veligers, which are microscopic and not visible to the human eye. As they mature they grow shells and attach to hard surfaces.

Zebra mussels entered United States waters in ship ballast. Barges may move them upstream on major rivers. Experts believe they enter impoundments when boats or docks with adult zebra mussels attached are moved from an infested lake to a new lake, or if lake water containing veligers is moved to another reservoir. Live wells and bilge pumps on boats, for instance, can hold water when boats are transported overland.

How zebra mussels entered Smithville Lake is uncertain, Banek said. In 2010, a cove near the Camp Branch Marina was treated to kill zebra mussel adults and larvae. That treatment came after adult zebra mussels were found on a boat lift at the marina that had been moved from another lake.

But biologists do not know if that case is linked to the recent find, and due to the lake’s large size and a heavy volume of boat traffic in a metro area, no determination will be possible.

There is no practical way to eliminate zebra mussels from large lakes once they are established, Banek said. Veligers float and travel in water currents. The Smithville Lake find means the zebra mussels will likely become established in the Little Platte River downstream of the lake’s dam, and in the Platte River downstream of its confluence with the Little Platte in Platte County. The Platte River enters the Missouri River upstream of Kansas City.

Zebra mussels are also present in the Kansas City suburbs at Lake Lotawana. They have been found in the past at a moat near the Isle of Capri Casino at Kansas City, and in small numbers at scattered locations along the Missouri River.

In Missouri, zebra mussels have been found at Lake of the Ozarks on the Osage River, and in Bull Shoals Lake and Lake Taneycomo in the White River system.

Zebra mussels have also been found in several locations in Kansas including lakes that feed into the Kansas River, which joins the Missouri River at Kansas City.

The Corps of Engineers is placing signs at the lake warning boaters that zebra mussels are present so they will take steps not to move the invaders. Boaters can play a major role in preventing the further spread of zebra mussels by making sure they clean, drain and dry their boats and trailers before moving them between lakes and rivers.

  • Clean – Remove all plants, animals and mud, and thoroughly wash everything, especially live wells, crevices and other hidden areas. If a boat doesn’t have a week to dry out before the next use, wash boat bilges, trailers, motor drive units and live wells with hot water at least 104 degrees. Most commercial car washers meet this standard.
  • Drain – Eliminate all water before leaving the area, including live wells, bilge and engine cooling water.
  • Dry – Allow boats and other equipment to dry in the sun at least five days before launching in other waters.

“The good thing is that Smithville Lake is only the fifth reservoir in Missouri where zebra mussels have been discovered,” Banek said. “The vast majority of Missouri's reservoirs are still free of zebra mussels and I hope we can keep them that way. Everyone moving boats or equipment from one reservoir to another should clean, drain and dry before launching.”

For more information on zebra mussels, visit or For more information on Smithville Lake, visit