Fish and Game to continue to monitor fish mortalities following quagga mussel treatment

Idaho Fish and Game biologists continue to monitor the mid-Snake River for fish mortalities following the chelated copper treatment after the detection of quagga mussel veligers in mid-September. The Idaho Department of Agriculture completed their 10-day quagga mussel treatment in the mid-Snake River on October 13.

As expected, the treatment, which was designed to eliminate quagga mussels, also resulted in both fish and aquatic plants dying within the treatment area. Fish and Game has detected thousands of dead fish within an approximately six-mile section of the river. The overwhelming majority of the mortalities have been largescale suckers, common carp and northern pikeminnow.

A small number of yellow perch and other pan fish mortalities have been detected.

White sturgeon have also been impacted by the treatment, with all detected sturgeon mortalities being hatchery-produced fish. Approximately 50 percent of the detected sturgeon have been stocked since 2015.

River recreationists that access the Snake River downstream of the “broken bridge” at Yingst Grade / Auger Park are encouraged to notify the Magic Valley Region at (208) 324-4359 if they find a sturgeon along the riverbank or floating in the river. Fisheries biologists will make every effort to locate the sturgeon to take important biological data from each fish found. 

Snake River closure reduced 

After the detection of the quagga mussel veligers, the Idaho Fish and Game Commission closed a 23-mile section of the mid-Snake River to all hunting, fishing and trapping below the highwater mark of the river in an attempt to stop the potential spread of the mussels. The closure extended from the Twin Falls Power Plant, downstream to the State Highway 46 bridge, also known as the Ken Curtis bridge. 

On Tuesday, October 17, the Commission removed the closure on hunting, fishing and trapping on the section of the mid-Snake River downstream of the “broken bridge” near Auger Falls effective at mid-night, October 19.

The river closure remains in effect upstream of the “broken bridge” to the Twin Falls Power Plant. The closure includes hunting, fishing and trapping as well as any water access by watercraft, people or pets within the approximately 10-mile section of river.

Ongoing fisheries monitoring

Fisheries biologists will continue to monitor impacts to fish populations over the coming months. Electrofishing surveys are planned over the coming weeks, which will help in understanding the impacts of the treatment on fish populations and guide efforts to rebuild fish populations.