Fish passage Egglfing-Obernberg

A LIFE Riverscape Lower Inn initiative to boost biodiversity

VERBUND is constructing a 5.8 km-long bypass channel at the Egglfing-Obernberg power station on the River Inn, to be completed by 2027. Preparations began as early as autumn 2024. In future, fish will be able to pass the power station, and new habitats for endangered species will be created.

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Aquatic Habitat Technical Details and Data

A near-natural aquatic habitat

Building on the positive experiences gained at the Ering-Frauenstein and Braunau-Simbach power stations on the River Inn, VERBUND has developed a similar concept for the construction of a fish passage at the Egglfing-Obernberg power station on the River Inn.

To enable fish to swim past the power station, a bypass channel with natural flow dynamics is being constructed. It extends from the upstream section to the downstream section of the river, downstream of the power station. The Malchinger Bach is also being integrated into the new watercourse. Downstream of the bypass channel’s confluence, the banks of the Inn are being renaturalised.

The fish migration aid is more than just a migration corridor: with fords, gravel banks shaped by the current, shallow water zones, deadwood and coves, a structurally rich watercourse is being created that offers an attractive habitat for numerous Inn fish and other aquatic organisms.

Shallow gravel banks serve as spawning grounds and resting places for young fish, whilst deeper areas provide space for large river fish such as the huchen. New habitats are being created around the bypass channel for gravel-nesting bird species, amphibians, reptiles, insects and typical floodplain vegetation. The bypass channel also ensures a better water supply to the adjacent floodplain and enhances its ecological value.

The fish migration aid will allow 4 to 10 cubic metres of water to flow per second. During the spawning season for most Inn fish, from spring to summer, more water flows; in autumn and winter, less. The water is channelled from the Inn into the fish migration aid via the supply structure; a controlled supplementary supply structure enables the flow rate to be increased seasonally. Over a total length of 5.8 kilometres, the water first flows down a ramp and, after joining the Malchinger Bach, through the floodplain forest. Between the power station and the road bridge, the bypass channel rejoins the River Inn. A gravel island is being created at the confluence, whilst downstream, the banks of the River Inn are being renaturalised to create a structurally rich environment over a length of around 1.7 kilometres.

Fish migration and the ecological development of the bypass channel and its surroundings are being documented through scientific monitoring, and the results are being published.

A comparable project at the Ering-Frauenstein Inn power station provides clear evidence that natural, dynamic and large-scale bypass channels are well received by fish. It came into operation in 2019, and by the end of 2020 a total of around 40,000 fish had swum past the power station. They belonged to 36 different fish species. The largest fish was a catfish measuring 1.2 metres in length. One of the highlights was also the detection of several specimens of the stone loach, a fish species previously thought to be extinct in the Lower Inn.

In the Lower Inn European Reserve, the LIFE project contributes to the implementation of the Fauna-Flora-Habitat Directive and the Birds Directive, as well as the European Union’s Water Framework Directive. The project is co-financed by the European Union through funds from the LIFE Programme.

Bypass watercourses and riverbank restoration
Technical details and data

Responsibility

Innwerk AG

Approval process

December 2019 to December 2025

Construction

March 2026 to the end of 2027
Commissioning and remaining works in 2028

The construction works will be carried out in the most environmentally and climate-friendly manner possible: excavated material will be reused on site to create new gravel habitats – thereby reducing transport distances and vehicle emissions to a minimum. Material movements of approximately 530,000 m³ are anticipated.

Location of the bypass watercourse: on the left (Bavarian) bank of the Inn between Inn km 40.6 and 34.8, entirely within the ‘Salzach and Lower Inn’ Habitats Directive (FFH) site, and partly within the ‘Salzach and Inn’ Special Protection Area (SPA). The Inn forms part of the RAMSAR site ‘Lower Inn, Haiming-Neuhaus’.

Length

5,8 km (unrolled)

Width of the water surface

7-10 m

Height difference

10,6 m at W30

Gradient

0,05 to 3,6 %

Flow rate

At least 4 m³/s to 10 m³/s (depending on the season)

4 m³/s (mid-November to mid-February)
otherwise between 4 and 10 m³/s (maximum in May)

Adjustments possible following fish ecology monitoring

Location of the bank restoration

1.65 km along the left (Bavarian) bank of the Inn
between Inn km 34.45 and 32.80