In Sweden, around 2,100 hydropower plants account for a climate-friendly alternative and over a third of all electricity.

But hydropower has also stopped migratory fish, drained rapids and destroyed ecosystems.

Bertil Svensson from Olofstorp outside Gothenburg has worked for an energy company and managed hydropower stations from 1984 onwards.

He tells Uppdrag granskning that the eel migration at that time was significantly larger than today - but that eel death is not a new phenomenon.

- There was not an eel that could pass, they went straight down into this container which had to be emptied a couple of times a year, because it was full of a mourning consisting of leaves and eels.

Many hundreds, maybe thousands, eels in total.

There are solutions

On average, 70% of the adult eels that swim into a hydropower plant die, according to studies and leading researchers on the subject.

- Of course I have a bad conscience, but that was just the way it was to run a station.

It was the back of the coin, in terms of the nice clean electricity.

They could have been carried around the eels and released on the underside.

But they are not afraid of it, there are three more stations before they reach Göta Älv and the sea, says Bertil Svensson.

The six largest power companies in Sweden merged in 2010 in a joint initiative called Krafttag ål.

The goal was to drastically reduce the mortality in the turbines, among other things by building nature-like fishing roads past the power plants and installing grids that will prevent eels from being hacked in the turbines.

If the power plants are not to be completely demolished, it is a complete solution with the two measures required for weak-swimming species such as eels, according to the research.

Vattenfall: "A trade-off"

But Assignment review has been able to tell that only four of the 380 power plants included in Krafttag eel have implemented the complete solution. 

Kraftbolaget Tekniska Verken has created one of the four complete solutions in Linköping.

- We have both a need in society for renewable electricity that we get from hydropower and a responsibility for biodiversity.

There are two values ​​we must constantly balance and it is not entirely easy, says Rebecka Hovenberg (MP), vice chairman at Kraftbolaget Tekniska Verken.

Erik Sparrevik at Vattenfall, chairman of Krafttag eel, says that it is not about a reluctance on the part of the companies that has meant that no one else has made a complete solution.

He says that a rebuild must work both operationally, cost-wise and from a safety point of view.

- At small power plants there is the knowledge to build past, at large power plants there is no knowledge.

Then there is a balance and balance with the electric power through hydropower that we also need.