Boku Study Shows How Hydropower Plants Can Be Operated More Gently for Fish

What Is Hydropeaking?

Over the course of roughly ten years, the researchers flooded their experimental facility – which simulates river sections and their landings such as small bays or basins that are cut off from the current when water levels drop – under different scenarios. The so-called hydropeaking impacts in flowing waters were simulated.

Fish of various sizes, as well as fish larvae, were placed in the water. The approximately 120,000 animals from four fish species coped particularly poorly with changes during nighttime hours. The rapid changes are especially problematic for juvenile fish, who are at risk of being stranded or being carried far downstream by the changes in water levels and currents.

The fish species did not influence the outcome – it was purely size, or smallness, that mattered. The smaller the fish were, the less they were able to protect themselves from stranding or other problems when water levels and flow velocities changed rapidly. The greater the disturbances, the more the juvenile fish suffered.

What the Researchers Recommend

Based on their observations and measurements, the researchers advocate that power plant operators allow the water level to recede as slowly as possible after a surge. This gives the fish more time to adjust.

Lead author Stefan Schmutz is also quoted with the recommendation: "Zusätzlich sollten nächtliche Spitzen vermieden und Kaltwasserstöße reduziert werden". When fish were exposed to multiple hydropeaking events, a small learning effect was observed in the animals, the researchers write in their paper.

Background on the Study

The investigations have, in any case, yielded basic principles with which power plant operations can be made as environmentally compatible as possible, according to the researchers. The publication is available online at https://doi.org/10.1038/s43247-026-03580-2, and information on the "HyTEC" research facility is available at https://hydropeaking.boku.ac.at.