Hydroelectricity plays an important role in keeping the grid humming throughout Europe. While wind and solar generate energy under some conditions, hydropower can start generating power whenever the grid needs it – so-called baseload energy. The big issue now is how to design hydropower technology with fish in mind. 

Europe is awash in hydropower plants. There are more than 21,000 of various sizes currently in operation, most of which are small plants generating less than 10MW, according to World Wildlife Fund (WWF) data from 2019.

For some countries, like Italy, hydropower is the only renewable way to generate baseload power.

But for fish species, hydroelectric dams represent a serious threat. Fish like the Atlantic salmon and sturgeon, driven to undertake lengthy migrations upstream to spawning grounds far from the ocean, are particularly at risk. In fact, for all fish species on average, more than one in five fish will die when passing through hydropower plants.

"They’re one of the main reasons we fail to meet our water framework directive goals," says Dr Christian Wolter, one of the researchers in FIThydro at the Leibniz Institute of Freshwater Ecology and Inland Fisheries.

An index to classify fish fatalities

'We had a national project where the nature conservancy agency developed mortality assessments for birds and bats at wind power stations, and we thought the same should be done for fish.' Dr Christian Wolter, Leibniz Institute for Freshwater Ecology and Inland Fisheries

Dr Wolter got the idea to develop an index to classify the mortality risks plants pose to fish from the wind power industry.  

"We had a national project where the nature conservancy agency developed mortality assessments for birds and bats at wind power stations, and we thought the same should be done for fish," he says.

To create the index, he examined river conditions, turbine types at hydroelectric dams, as well as the ambient fish population and the biology of the species living there. The results showed that some of the greatest harm came from plants that contribute the least power to the grid.

"In Germany for example, we have 7,800 hydropower plants, and 436 of them have a generation capacity of 1MW or more…producing 84% of the renewable energy," says Dr Wolter.

"For the small plants, we see no serious contribution to renewable energy...but significant harm to free-flowing rivers, aquatic biodiversity, because they are often in the headwaters where the spawning grounds of the migratory fish are [the sturgeon, the salmon]."

What’s more, because of their low volume of water, small hydropower plants can be less effective as coveted baseload plants, since they can be as volatile as wind or solar.

"The smallest hydropower is most incentivised, and this is completely counterproductive," says Dr Wolter.

"Our plea is to support a few large hydropower plants rather than many, many small power plants."

For plants to operate in a fish-friendly way, Dr Wolter says they must also be willing to consider building in fish protection tools to help at-risk species. They can then use the mortality index to examine what impact these mitigation measures would have on lowering risks.

Fish-friendly guidance systems

FIThydro project coordinator Dr Peter Rutschmann oversaw the development of some of these new mitigation measures. A number of hydropower plants lack effective means to aid fish that are migrating downstream, requiring new ways to make sure they take a path that doesn’t put them in danger.

Many methods rely on trying to work with natural fish behaviour, so that they will be guided away from turbine intakes. One of the simplest tools involved used racks of curved bars.

"The fish will not pass these coarse bars because there are vortices shedding from them, and this is something fish try to avoid. Fish do not like to swim through shear zones."

Dr Rutschmann’s team took the principle a step further, investigating fish in the laboratory at the Technical University of Munich to create a tool known as Induced Drift Application (IDA).

Flushing fish through the turbine

"We noticed that the very bad swimmers were less affected by the turbines, and we realised that it is probably that they can’t resist the flow," says Dr Rutschmann. Other fish like salmon, which are good swimmers, may fight the water passage and stay in the turbine longer, increasing mortality rates.

"We had the idea to give fish an electroshock…so they were paralysed for a few seconds and would be flushed through the turbine." They also found out that fish tend to swim to the electric anode and that fish who passed through closer to the centre of a turbine have the least mortality risk. By placing an anode at the right spot, fish were able to pass through more safely.

"It’s a simple [inexpensive] device which you can use for any existing turbine, and you can reduce mortality to say 50%."

Measures to Improve Fish Passage Through a Turbine © Geiger, Franz; Rutschmann, Peter; Stoltz, Ulli (2022)

Changing mindsets to save fish

'It’s a simple (inexpensive) device which you can use for any existing turbine, and you can reduce mortality to say 50%.' Dr Peter Rutschmann, Technical University of Munich

What it all comes down to, say the researchers, is encouraging operators to run their plant in a smarter, more fish-friendly way. It also can mean redefining some of best practices to include fish and ecological welfare.

"Free flowing rivers are a common good. Allowing for hydropower should not necessarily imply that they can use every drop of the river. If licences were awarded in a way that 10% of the average discharge of the river should be reserved for ecological purposes, and the remaining 90% could be used for hydropower, there would be sufficient water for all purposes. Right now, the situation is such that any water not used for electricity production is counted as a loss," says Dr Wolter.

Dr Rutschmann says that operators must factor in not just optimising energy, but also fish survival into their performance forecasts to produce truly fish-friendly power. He suggests operating in a way that is more in synch with aquatic populations and releasing more water when they most need it.

"I see a trend in hydropower which goes in the direction that you operate based on what happens in the river, with 3D ultrasound tracking, for example. You see there is a swarm of fish approaching a hydropower plant, and then…you can do something like open the spillway or shut down the turbines. And when the swarm has passed you can operate the power plant as before."

By using new technologies, they say, countries can balance waterway and biodiversity protection with European Green Deal goals to increase renewable power.