A deadly fish virus previously affecting largemouth bass in southern Michigan waters has spread to smallmouth bass in northern Lower Peninsula inland lakes.

Michigan Department of Natural Resources identified largemouth bass virus in three counties bordering Lake Huron. A fish kill last fall in Iosco County’s Cedar Lake prompted studies of fish kill in Alpena County’s Beaver Lake and Montmorency’s Avalon Lake. The virus was discovered in smallmouth bass in both lakes. Downstate outbreaks of the disease in the early 2000s killed 10 to 20 percent of the adult largemouth bass exposed to the pathogen. The potential spread to northwest Michigan waters raises DNR and angler concerns about local bass fisheries.

Bassmaster magazine’s 2018 top 100 bass lakes in the country ranked Grand Traverse Bay no. 10 in the nation’s northeast region. Glen, Long, Duck, Green, Boardman and Cedar lakes are also among the area’s top bass fisheries, said DNR Fisheries Management Biologist Heather Hettinger of the Traverse City Customer Service Center. She noted that the region’s lakes primarily support smallmouth bass, although largemouth bass also exist in area lakes.

Traverse City Bass Destination Charter Captain Butch Derickson offers four to five charters per week during bass season. His charters frequent East and West Bay, Skegemog, Elk, Torch, Crystal, Big Platte and Lake Leelanau. Derickson said 90 percent of the fishing is for smallmouth bass.

“Bass fishing is a tremendous resource and we need to protect it,” he said.

Derickson has observed bass caught on his charters in recent years appeared healthy and the population appears growing. Hettinger supports his observations.

“My division has spent quite a bit of time in the last few years surveying the popular bass lakes in Grand Traverse and Leelanau counties,” Hettinger said. “There have been no reports of die-offs exclusive to large or smallmouth bass.”

Fish kill is a primary method of identifying the virus’ presence in lakes, but the disease has been found in waters without reported fish kills, according to DNR reports.

The DNR documents state affected fish appear normal but may swim more slowly or appear nonresponsive to stimuli as a result of the disease’s impact on the fish swim bladder. Dying infected fish may be seen near the water’s surface and show trouble remaining upright. Bass, Michigan bluegill and black crappie carry the disease, but it’s not fatal for bluegill and black crappie.

The pathogen’s toll on a fish population can be influenced by stress factors, including aquatic weed treatment, spawning and water temperature.

“Even with our deep, cool waters, we get temperature ranges that stress fish,” said Hettinger.

Largemouth bass virus cannot be eradicated from lakes and there is no treatment for infected fish. DNR biologists believe boaters and anglers play a key role in introducing the virus into a lake and also in protecting the region’s fish. People who relocate live fish to boost the population in their favorite lake can unknowingly transfer the disease between bodies of water.

“It’s one of the reasons it’s illegal in Michigan,” said Hettinger.

Dave Borgeson, the DNR’s Gaylord-based Northern Lake Huron supervisor for the fisheries division recognizes outdoor enthusiasts enjoy lake hopping with their boats to experience different bodies of waters. He said that’s where fish protection begins.

“It all goes back to the safe boating practices that we’ve preached forever,” said Borgeson. Standard practices include disinfecting your boat and cleaning all fishing gear between trips.

“It takes a large level of compliance for that to work,” he said. “Some people don’t know or care enough, it is sad to say.”

Boaters, anglers and those living or recreating along a lake can aid the DNR in identifying fish populations potentially infected with largemouth bass virus.

“If you notice a significant number of dead fish, report it as quickly as possible to the local DNR management unit,” Borgeson advises. “We need viable, fresh fish to test.”

Fish kills may also be reported online at michigan.gov/eyesinthefield.