Reichenau power plant: a clear path for lake trout

Several floods in 2019/20 had caused erosion in the river bed of the Alpine Rhine, making it almost impossible for the fish pass, built in 2000, to be reached. Thanks to the excellent coordination of all the parties involved, the restoration of access to the fish ladder was carried out in an accelerated procedure. And it is a success story: the number of ascending lake trout, as recorded by the annual trap catches, has increased sevenfold.

Every year, lake trout migrate from Lake Constance to the Rhine to spawn in its source rivers. But the route is not always passable. Since 2019/20, there has been an obstacle at the Reichenau power plant. After erosion of the river bed by flooding, the fish could no longer reach the fish ladder under residual flow conditions. But now there is good news for the endangered fish species. Extensive rehabilitation has restored free passage.

A vital migration route for lake trout

Lake trout are among the most fascinating fish species in our waters. Born in the clear upper reaches of the Alpine Rhine, young trout migrate to Lake Constance, where they grow up before returning to their native waters years later to reproduce. But their migration is often beset with obstacles, and they have to overcome weirs and power plants.

Special fish ladders have been installed at the Reichenau power plant so that the lake trout can reach their spawning grounds. Since 2000, a fish ladder has enabled the fish to pass through the plant. But in 2019 and 2020, severe flooding caused extensive erosion of the riverbed just before the entrance to the fish ladder, interrupting migration when water levels were low. 

The urgent need for restoration

The lake trout in particular relies on this access. It is on the Red List of endangered species, and its population has declined sharply in recent decades. A remediation project was launched to restore the fish's ability to migrate. The project was based on a decision by the Graubünden cantonal government that obliged Kraftwerke Reichenau AG to restore the fish ladder at the counterweir of the Reichenau dam. The Graubünden Office for Hunting and Fishing (AJF), the Federal Office for the Environment (BAFU), Kraftwerke Reichenau AG and Axpo's environmental department then worked closely together to quickly find a sustainable solution.

An ambitious construction project

The remediation was carried out at a rapid pace. Within just one year, Axpo's specialists planned and implemented a solution in the form of a fish-friendly block ramp. This ramp consists of large natural stones arranged in such a way that they can withstand flooding and also offer fish a passable route at low tide in specially designed channels. After rapid planning and official approval, the construction work was completed by the end of summer 2022 – just in time for the main migration season of lake trout in autumn.

Success across the board

The block ramp has been closely monitored since it was put into operation. Technical measurements were taken to check the flow velocities and water depths, while automatic counting stations and trap catches documented fish migration. The results speak for themselves: the block ramp is stable and works perfectly. Furthermore, it has remained stable despite several major flood events since it was put into operation. Particularly encouraging: the number of ascending lake trout, as recorded by the annual trap catches, increased sevenfold from 2020 to 2024 – from 40 to 286 animals. There was also evidence of an increase in smaller fish, which proves that the ramp is suitable for fish of different sizes.

The successful renovation of the fish ladder at the Reichenau power plant shows that major ecological improvements can be achieved through commitment and collaboration. The lake trout now has the opportunity to reach its spawning grounds unhindered – a significant success for species protection and biodiversity in our waters.