Zebra Mussels Confirmed in Lake Francis Case

October 23, 2019

Pierre, S.D. – The South Dakota Department of Game, Fish and Parks (GFP) has confirmed the presence of adult zebra mussels in Lake Francis Case.

“The invasive mussels were found on plate samplers attached to docks and also along shoreline areas,” said Chamberlain Area Fisheries Supervisor Chris Longhenry. “Densities are low in Lake Francis Case at this time, but the mussels are widespread and present through most of the reservoir.”

Lake Francis Case will now be classified as infested with zebra mussels. In July 2019, zebra mussels were confirmed in Lake Sharpe, another mainstem Missouri River reservoir located upstream from Lake Francis Case. Reproducing populations of zebra mussels were discovered in Lewis and Clark Lake and in the Missouri River below Gavins Point Dam in 2015.

Waters infested with zebra mussels are designated as containment waters. Specific decontamination requirements exist for boats kept in these waters continuously for three or more days, or that cannot have all water drained from them.

“Boaters with watercraft that fall into these categories need to learn how to properly decontaminate their boats to slow the spread of zebra mussels,” said Longhenry.

Every time they leave the water, all boaters and anglers should:

  • Clean watercraft and trailers of all aquatic plants and mud
  • Drain all water by removing all drains, plugs, bailers, or valves that retain water
  • Dispose of unwanted bait in trash or fish cleaning stations when leaving the water

Completely draining a boat is the first step in making sure invasive species are not transferred to other waters.

For more information on zebra mussels, other aquatic invasive species, and how to properly decontaminate your watercraft, visit


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