The river section between the hydropower plants of Abwinden-Asten and Wallsee- Mitterkirchen is still one of the most interesting along the Upper Austrian Danube in terms of aquaculture and fishing, even though numerous river engineering works in the past have left their traces. A major river training project towards the end of the 19th century caused a flow concentration to one main arm, and the hydropower impoundment negatively affected the quality of the habitats. Transverse training structures have since then obstructed the passage of important Danube fish species such as nase, barbel and huchen.
The deepening of the river bed near the reservoir’s water inlet, the progressing erosion resulting from a lack of bed load and the construction of lateral dikes in the central reservoir area have largely disconnected the river side arms from the main stream.
This has decreased the habitats of fish species that prefer slow-flowing water zones and has concurrently blocked their passage to vital spawning grounds. Extensive gravel mining operations in this Danube section have additionally caused a dramatic structural decline. The growing popularity of ship transport (especially cruise ships) has aggravated the problem of wave wash, which mainly affects the larvae and young of certain fish species that spawn over gravel.
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(Source: aqua press Int. 4/2009)
