New paper - improving the eel migration route in a hydropower regulated river

Our new paper on downstream migration of European eel (Anguilla anguilla) is out, and the main finding is surprisingly simple: a small tweak to a hydropower intake can make a big difference for eel survival.

At Fosstveit Hydropower Plant in southern Norway, survival of silver eels jumped from roughly 50–70% to 100% after the intake was retrofitted. For a critically endangered species, that’s huge.

European eels grow up in our rivers and lakes before heading all the way to the Sargasso Sea to spawn, a very long migration. But hydropower plants sit on many of these routes, and turbines are especially deadly for long, flexible fish like eels. Earlier work at Fosstveit (2012–2013) showed high turbine mortality. Even with a bottom bypass, far too many eels didn’t make it through.

In 2024 the intake was rebuilt with three key features:

• a low‑inclined rack (29°)

• 15 mm bar spacing

• a surface bypass

The goal was straightforward: keep eels out of the turbines and guide them safely to the bypass instead. And it worked! We tracked acoustically tagged silver eels in 2024–2025, and every eel passed safely and continued downstream to the river mouth. Migration still slowed a bit at the plant, so there’s more to learn, but the survival improvement is clear.

This study shows that a relatively modest engineering solution can remove turbine mortality almost entirely. With so many hydropower plants across Europe, similar upgrades could help restore safer migration routes for European eel.

You can read the paper here!

This study was financed by Småkraft AS, NVE, and the County Governor of Agder.