Aare in Seftau Bremgarten: ecologically upgraded

The section of the Aare between Seftau in the municipality of Bremgarten and the Halen Bridge near Herrenschwanden in the municipality of Kirchlindach is around two kilometres long. Dredging and construction work began here in October 2024, and the work was completed in April 2025. The reasons for the project were flood protection, as the structures on the right bank of the Aare had become outdated, as well as the change to the concession section and its return to the canton in perfect condition.

An ecological upgrade was also sensible and necessary, as this section of the Aare is of national importance for grayling. The fish, which are around 40 centimetres long, are on Switzerland’s Red List of endangered animal species. Until now, the larvae had found little habitat in the heavily engineered bank sections. The newly created structures along this stretch are particularly important for the grayling population: shallow-water zones have been created for young fish, while adult fish thrive in fast-flowing sections. In addition, the critically endangered brook lamprey is finding a suitable habitat in the newly forming sandy areas. Its eyeless larvae (ammocoetes) spend three to five years buried in the sand before developing through metamorphosis into adult animals with eyes. They then reproduce on loose, fine-gravel substrate with good water flow and subsequently die.

Rootstocks, deadwood, gravel and stones

Along the entire section, the construction workers placed rootstocks, deadwood, gravel and stones, both on the bank and in the riverbed. In the Seftau area, the bank was flattened, giving the Aare more space. In some places, the riverside path was moved further inland.

Insects, frogs and water birds find habitats in such river landscapes that they do not have in built-up bodies of water. In total, around 2.5 million francs were invested in the project. The ecological measures accounted for half of the construction costs. These costs were borne in equal thirds by the BKW eco-fund, the renaturation fund of the Canton of Bern and the “naturemade” EWB (Energie Wasser Bern) eco-fund. The other half of the construction costs for flood protection was shared by the Confederation, the Canton of Bern, BKW and the municipality of Bremgarten.

Great interest in the guided tours

On 15 March 2025, the developers invited people to an open day at the construction site. During two guided tours, they showed and explained what had been built and for what purpose. At the end, free refreshments were provided. Despite the cold, wet weather, more than 100 people came both before and after midday. A common remark among visitors was: “Wow, a lot has happened here!” The widened path and the ecological measures were described as successful and impressed people. However, some locals also expressed concern that this success could become something of a boomerang – namely that the new Seftau could attract even more visitors.

Further insights into the project in Bremgarten

With the relicensing of the Mühleberg hydroelectric power plant, the maintenance obligation for the banks of the Aare has transferred from BKW back to the Canton of Bern, specifically for the section from the water return of the Felsenau power plant to the Halen Bridge. BKW was therefore asked to hand over the section of the Aare in a “defect-free” condition. Since 2018, the condition of the section has been evaluated and the need for action determined. This formed the basis for the project that has now been implemented.

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