"There is the rattling of the muhle on the rushing brook. Klipp, klapp." As romantic as it is in the folk song "die muhle" nowadays, animal protectors can no longer describe the work of the mullers: "the wheels run swiftly and grind the wheat into flour so fine for us. Klipp klapp." The water wheels have long since ceased to produce flour for baking bread, but they still produce something vital: electricity. And that's what they're doing in the spirit of the times: sustainable and climate-neutral, close to consumers and decentralized.
The criticism from the fishing association, however, is that when the turbine shovels the water around, the fish increasingly get caught between the wheels. In particular, it should concern the eel, which needs an unobstructed path to spawn in the distant saragossa sea, near the bahamas.
Chopped up cadavers: no sign of them
On the internet and in tv reports there is often talk of a real bloodbath with masses of chopped fish. Buckets full of dead animals can be seen. "If a fish gets caught in the turbines, its chance of survival is very slim. Only about ten percent survive it", says fritz loscher-fruhwald, president of the fishing association of central franconia.
Electricity is also generated on the aisch. One of the watermullers is georg ortegel, who runs the greiendorf muhle. The 75 year old grew up in the muhle. Electricity has been produced here for over a hundred years. Formerly exclusively for the people of greiendorf, today with feed-in to the grid. When asked about chopped up fish, the 75-year-old immediately waves it off: "we don't have this problem at all." A few eels are seen each year that have pressure marks from the paddlewheels. But mass fish kills, even chopped up carcasses, have never occurred before. All the dead fish that he sees are dead and sick animals washed up in front of the protection rake.
How wide must be the rake?
"Technically, it is impossible for the fish to get through", says ortegel. He stands on the footbridge of his barrage and points into the water. There is a reddish-brown grating sticking out of the water. The approximately five-meter-wide rake, through which the aisch water rushes down 1.60 meters, prevents the fish from moving forward. The distance between the struts is two centimeters. A width that is just about bearable for fritz loscher-fruhwald of the fishery association: "there are old power plants whose rakes have up to five centimeters of permeability." Quite a few fish got through here. It is particularly problematic for eel and younger fish: only a maximum rake width of 1.5 centimeters prevents them from slipping through, says loscher-fruhwald .
Fish ladder ensures animal welfare
According to the fisheries advisory service of the district of central franconia, the 20 or so power plants on the aisch river are sufficient to ensure that not a single eel reaches its destination on its journey – despite detailed eu eel protection regulations. In 2006, ortegel built a fish ladder for his hydroelectric power plant between sterpersdorf and hochstadt as a protective measure. Over 16 steps a creek has since flowed as a bypass for the fishes.
Including planning and expert opinions, ortegel has invested more than 20,000 euros in the construction of the near-natural fish ladder. Since then, he has been getting double the feed-in tariff: without the fish ladder, it was two cents per kilowatt hour; now it's four cents. The greiendorfer muhle is one of the few on the aisch river to have such a detour. Ortegel is exemplary in this respect as a hydroelectric power plant operator.
But does this measure make a difference?? "On the main, where the big power companies run their hydroelectric plants, the fish passes are most needed", says the greiendorfer. He could also imagine the masses of dead fish there. Ortegel is sure that the rake and the fish ladder will provide the best possible protection for his plant. For the specialist fisheries consultancy, which also prepares the expert reports for the fish ladders, the type of turbine used and the amount of water in the river used by the facility are the key factors in assessing whether the eel is in danger. As far as the actual numbers of eels and dead animals on the aisch are concerned, however, the advisory office is fishing in the mud. There are no financial means for the necessary sample fishing.
Klaus muller, chairman of the hochstadt fishing association, is also familiar with the discussion about fish ladders and eel migrations: "the transverse structures of the power plants block the way for the eels." In his opinion, the fish ladders are a sensible measure. However, he also assumes that only a rake distance of at most one to 1.5 centimeters protects the eels.
So a retrofit of all power plants with narrower rakes would help? According to the fishery consultant, this would be an investment that could make decentralized hydropower unprofitable. What needs to be done to ensure that the eels can continue to swim to mate and the mills continue to rattle at the same time is probably in the hands of politics.