If the Gudena River were a car up for inspection, it would fail with a bang: New project aims to save water quality

For over 150 years, the Guden River near Vestbirk has been used for hydroelectric power, but today, work begins to restore it to its original course.

The plan is to transition from power production to creating a better habitat for plants and animals as part of Denmark’s largest EU-supported water project, now underway northwest of Horsens.

Horsens Municipality and the Nature Agency are taking the first steps, beginning excavation work to recreate the river’s natural flow through the area, benefiting fish, small animals, and plants alike.

One reason for restoring the river’s original course is that its water quality has deteriorated, says Peter Eskildsen, project leader in Horsens Municipality.

“Our rivers, lakes, and fjords have certain biological quality standards they must meet. For rivers, biologists examine aquatic insects, fish, and plants. It’s like a car failing its inspection because it can’t brake—Guden River is failing with a bang,” he explains.

Around nine kilometers of the Guden River will, through this project, return as closely as possible to its original path. As part of the initiative, Bredvad Lake will be divided into two by a 1.7-kilometer-long dam. This way, the eastern section of the lake will be preserved, while the restored river will flow through the abandoned western part.

“At the bottom of the western side lies the river’s original course. A 10 to 12-meter-wide riverbed will reemerge, with relatively fast-flowing water by Danish standards. No one has seen this in 100 years, and there are no images of it—so it will be quite exciting,” says Peter Eskildsen.

Mayor of Horsens, Peter Sørensen, is pleased with the project.

“The Guden River will return to its state from 100 years ago, along with all the life that existed then. The goal is to create more biodiversity and a better aquatic environment,” he says.

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**Expecting more trout in the Guden River**

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The dam will take shape during spring 2026, followed by the excavation of the river along the lake.

The project will improve conditions for flora and fauna, creating spawning grounds and free passage for fish in the Guden River.

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**Changes over the last 100 years**

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The use of the Guden River’s flow over the past 100 years has brought significant changes to the Vestbirk area:

- A barrier dam across the Guden River created three artificial lakes.

- The impounded lakes affect a 3.6-kilometer stretch of the Guden River upstream from the lakes, increasing depth and reducing flow speed. The original riverbed, made of stones and gravel, now lies buried under sand and silt.

- A two-kilometer stretch of the Guden River (the "Dead River") beneath the rediscovered bridge currently carries only about 20 percent of its natural flow.

- A 900-meter stretch near the power plant has been completely dry since 1924. The river’s total drop of 10 meters over approximately 9 kilometers is now concentrated in the hydroelectric plant’s turbine.

The river restoration project at Vestbirk will address all the above points by recreating the original Guden River.

Source: Horsens Municipality

A previous barrier removal at Vilholt Mill resulted in a massive increase in fish numbers upstream of the barrier. Horsens Municipality therefore expects a similar rise in fish populations along this stretch of the Guden River once the project is complete.

“There will be significant gains for the trout population in the river. Currently, we find between two and ten trout per 100 meters, but we expect between 500 and 1,000 fish per 100 meters after restoration,” says Peter Eskildsen.

Forest ranger Søren Hald from the Nature Agency also welcomes the free-flowing water, which will benefit lake trout in the Guden River.

“We’ll have a riverbed that is quite unique in Denmark, with fast-flowing water in its natural course. It’s as close as we can get to having a river in Denmark,” he says.

70 percent of the restoration project “Vestbirk” is financed by EU funds from the European Maritime, Fisheries, and Aquaculture Fund, while the remaining 30 percent comes from national resources.

Excavation work has paused today due to frost. *(Photo: © Emil August Prehn)*

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