Bavarian Inn River to become passable to fish for first time in a century

Celebratory groundbreaking ceremony for the new fish pass at the VERBUND Inn power plant in Rosenheim

VERBUND is pressing ahead with the restoration of the Bavarian Inn River to its natural state and celebrating the groundbreaking ceremony for the construction of a 2.2-kilometre bypass at the Rosenheim power plant. 

More than a hundred years ago, human activity began to transform the wetlands of the Inn River into usable landscapes: floods were stopped in their tracks by engineered structures, floodplains were developed and used for agriculture and urban development, and the electricity required to power the economic boom was generated locally in hydropower plants. Biodiversity suffered particularly badly as a result of this activity.

As part of the implementation of the EU Water Framework Directive, VERBUND set up a comprehensive restoration programme for the areas surrounding of its hydropower plants on the Bavarian Inn River. The groundbreaking ceremony for the fish pass at the Rosenheim power plant marks the highlight of this ambitious environmental programme: once completed in the spring of 2027, the Bavarian Inn River will once again be completely passable for fish and other aquatic life in the section between Rosenheim and Stammham. In addition, previously separated habitats will once again be reconnected and new habitats created along the river banks, which have been heavily built up for decades. 

Inaugural event 

At the Rosenheim power plant, VERBUND will build a bypass to replicate natural conditions over the next one and a half years, which – thanks to its ecological design – will not only allow fish to bypass this section of the river, but also create new spawning grounds and refuges for the vast array of fish species and aquatic life native to the Inn River. 

The ceremonial groundbreaking ceremony for the construction of this fish pass was held on 11th July 2025 and was attended by high-ranking regional political representatives together with the project partners and employees: “Hydropower is a key technology for the energy transition. Targeted environmental measures such as fish passes enable us to strike a harmonious balance between generating renewable energy and protecting our valuable aquatic ecosystems,” explains Sabine Kahle-Sander, Vice President of the Government of Upper Bavaria in her welcoming address. 

“Changes to the course of the river and the construction of barrages at the beginning of the 20th century not only destroyed the ecological structures native to the riparian zone, but also prevented fish and other aquatic life from passing the Inn River,” explains Andreas March, Mayor of Rosenheim. “The groundbreaking ceremony for the new fish pass marks a new chapter in the river's history, with fish now able to once again travel up and down the river. Alongside this development, the rehabilitation of the riparian zones will once again create an environment that simulates a natural body of watering, restoring the habitat of the fauna and flora native to the Inn.”

Otto Lederer, District Administrator for Rosenheim County: “Constructive and solution-driven cooperation between power plant operators and the fishing industry is crucial in my opinion. The new fish pass marks a further milestone for the region’s ecological development and creates valuable habitats for all animals, flora and fauna found along the Inn River. I would like to express my sincere thanks to VERBUND and all other stakeholders for the pioneering balance achieved between sustainable energy generation and active nature conservation.”

Inn River to become passable to fish for first time in a century

At the heart of this eco-project is the construction of a 2.2-kilometre bypass that mimics natural conditions on the left bank of the Inn River. Equipped with meandering curves featuring different flow rates and water depths, the bypass will enable all fish and aquatic life to swim around the power plant while overcoming a height difference of 8.3 metres. The addition of gravel beds, sediment bars and felled trees will create an attractive habitat with new shelter and spawning grounds. 

“Once the fish pass is completed, from 2027 onwards the Bavarian Inn River will once again be completely passable for fish and other aquatic life for the first time since the construction of the power plants over a century ago. The other power plants have already reached this point, and today we are kicking off the preparatory work at the Rosenheim power plant,” outlines Karl Heinz Gruber, Managing Director of VERBUND Innkraftwerke “The plans for this latest installation draw on all our experience gained from the construction of over 70 fish passes in the past two decades. Over the next year and a half, a semi-natural river bypass will be constructed here with a seasonally adjusted flow rate that meets all the ecological requirements to the best possible extent. ”;

New habitat for fish, birds and reptiles

The environmental significance of the environmental measures being undertaken at the Rosenheim power plant in terms of nature conservation extends well beyond the ability of fish to move up and down the Inn River unobstructed. This project will result in the creation of a valuable habitat for plants native to riparian zones, as well as habitats for fish, aquatic life, water bird species and reptiles across the entire area of the bypass channel and nearby floodplains 

Millions invested in greening measures

“By 2027, VERBUND plans to invest roughly EUR 400 million on restoration measures, fish passes and habitat improvement at its hydropower plants in Bavaria and Austria. Half of these measures have already been implemented, resulting in 75% of all relevant power plants now being passable,” explains Michael Amerer, Managing Director of VERBUND Innkraftwerke. “We have earmarked EUR 100 million for projects at our 22 run-of-river power plants in Bavaria and along the Bavarian and Austrian borders – a third of which has already been spent. The overall success of the work completed to date has been verified by the fact that one third of the land area has been designated as a nature reserve since the construction of the power plants.”

Fish passes work!

State-of-the-art fish monitoring uses scientific data to demonstrate that fish passes and bypasses are accepted by fish. Any fish that pass through are recorded and entered into a database. This provides us with precise data on the number and species of fish and on migration. At VERBUND’s Ering-Frauenstein power plant on the Inn River, for example, a total of around 40,000 fish were recorded travelling through the power plant in the first year after it was commissioned in 2019. This figure includes 36 different species of fish, the largest fish being a 1.2-metre catfish. 

Facts and figures on the Rosenheim fish pass 

• Length: 2,215 m, Width: 8.6 to approx. 34 m (in the vicinity of local island structures)
• Water depth: Between a minimum of 0.4 m and approx. 1.2 m 
• Height difference: 8.3 mFlow rate: Variable amount based on natural, dynamic outflows of a floodplain stream: Basic flow rate generally 1.5 m³/s, variable additional flow rate up to a maximum of 4.0 m³/s.
• In addition, possibility of temporary flushing (flushing of spawning grounds, promotion of sediment redistribution with highest flushing discharge of 6.0 m³/s)
• Design elements: Gravel rapids, felled trees, rootstocks, sediment bars for fishes and birds, shallow water zones, nesting sites and piles of stones for reptiles, etc.