Signs of Emerald Ash Borer infestation at Nevers Dam, St. Croix River, November 19, 2025. (Russ Hanson)

A non-native insect that is killing countless trees, emerald ash borer, has made its way at least as far up the St. Croix River as the historic Nevers Dam site on the St. Croix River. Russ Hanson, The River Road Rambler, reports seeing evidence of the insect at that point on a recent survey he made in the area. The bugs kill almost every ash tree they contact, and have already devastated areas along the lower river.

“Several are showing the distinctive pale, flaky bark—usually the first sign you can see from the road,” Hanson wrote on his blog, River Road Ramblings. With his own farm about four miles away from the location, Hanson expects his ash trees to fall victim to the insects in the next couple years. He also compared the impact to the mass loss of elm trees caused by Dutch elm disease.

“Unlike the elm, which now survives mostly as a brush tree living only a decade or two at best, ash does not seem to regenerate well after borer attack,” he wrote. “We may be watching the quiet disappearance of a major species from our forests.”

Far from home

Emerald ash borers are native to northeast Asia, including Russia, Mongolia, northern China, Japan, and Korea. They are believed to have been first brought to North America in wood products. The first confirmed observation in North America was in Michigan in 2002. Since then it has been spreading throughout the United States and Canada.

The invasive insect does not travel far or fast on its own. It is spread across great distances by transporting firewood. Humans have made it possible for the insects to invade large areas of the country.

The first confirmed sighting in Wisconsin was in 2008. It was found in Burnett County last year, the last of the state’s 72 counties to report infestation. Emerald ash borer was first found in Minnesota in 2009 and has spread to most of the state’s forested counties.

St. Croix Valley infestation

Minnesota also publishes data that makes it possible to inspect individual reports of the species. (I could not find similar data for Wisconsin, if it exists). It helps trace Emerald Ash Borer’s possible path to Nevers Dam. The dam site on the Wisconsin side, where the National Park Service has a boat landing, parking, and bathrooms, is a popular place for fishing and campfires and the insect could have arrived directly from elsewhere in Wisconsin.

Emerald ash borer was first reported across the river from Nevers Dam in February 2024 at Wild River State Park, near the main park boat landing, about a mile downstream of the site where Hanson recently observed its impact. It was likely brought by park users bringing in firewood despite prohibitions. It may have spread from there across the river to Nevers Dam, or it could have been in reverse.

Ash is a widespread species, with an estimated billion trees of the species in Minnesota alone. Northwest Wisconsin has the highest percentage of ash of any region in the state.

Russ Hanson says he has many ash trees in his 50 acres of forest at his farm. He has plans to make the most of their eventual death.

“With a bandsaw mill handy, I’m hoping to salvage some of the ash as lumber and use the rest for firewood in the maple sap cooker,” Hanson wrote.