Over 800,000 readers this year!

Wyoming reservoir closing to boats due to invasive zebra mussel discovery in South Dakota


CASPER, Wyo. — The LAK Reservoir east of Newcastle, Wyoming, will be closed to watercraft starting 8 a.m. Monday, Aug. 1 due to the recent discovery of zebra mussels in Pactola Reservoir 27 miles from the Wyoming border in the Black Hills in South Dakota, according to the Wyoming Game and Fish Department.

The LAK Reservoir will remain closed to all motorized and non-motorized watercraft until the end of 2022. The decision to close the reservoir was made in consultation with True Ranches, according to Game and Fish. People will still be able to fish from the shore and ice fish in winter.

With Pactola Reservoir just 62 miles from LAK Reservoir, Game and Fish said it would be easy for invasive mussels to spread between the two waterbodies as the mussels can be spread from a little water left standing in a boat, even in the mussels’ microscopic state. Adult mussels are able to easily spread as they can live up to 30 days out of water and can attach to hard surfaces, Game and Fish added.


“South Dakota’s recent discovery of zebra mussels in Pactola significantly increased the threat of aquatic invasive species to Wyoming’s waters,” said Sheridan Region Fisheries Supervisor Paul Mavrakis in Game and Fish’s release. “True Ranches has generously allowed anglers and boaters access to their privately-owned reservoir for many years. However, this new development requires us to respond quickly to protect the reservoir and Wyoming from a possible zebra mussel introduction.”

The LAK Reservoir is on True Ranches property, but public access is provided through an access agreement. It offers about 122 surface acres that are fed by Stockade Beaver Creek and contain walleye smallmouth bass, tiger musky and other warm-water fish species, according to Game and Fish. The ranch uses it for irrigation purposes.

If invasive mussels were to get into the LAK Reservoir, it could have damaging consequences for the ecosystem and for the ranch, according to Game and Fish.


“If zebra mussels were to get introduced and become established, they will likely reproduce exponentially, negatively affecting the fishery, and could damage the water infrastructure the ranch relies on to irrigate,” said Sheridan Region AIS Specialist Reed Moore. “In the coming months, we will work with True Ranches to evaluate options for 2023 to mitigate the AIS threat to the reservoir and other waters in northeast Wyoming.”

Game and Fish said that the discovery of invasive mussels in Pactola Reservoir is a threat to other waterbodies in Wyoming. LAK Reservoir does not have an Aquatic Invasive Species check station to check and decontaminate boats.

Cleaning, draining and drying watercraft and equipment between waters is the most effective way to prevent moving AIS to new locations,” Game and Fish said.