Scientists from the Technische Universitaet Muenchen say fish species diversity in the area upstream of dams and weirs show a significant decline, one-quarter lower on average than downstream.
The interruption of a river course, whether for the generation of electricity, for flood protection or collection of drinking water, has greater effects on the biodiversity than the geological origin of the river itself, a TUM release said Wednesday.
Dams and weirs particularly affect current-loving fish, many of them endangered species.
"Brown trout, grayling and Danube salmon are demanding fish species that require oxygen-rich water and spawn in coarse gravel areas," Juergen Geist, TUM professor of aquatic systems biology, said.
"As typical residents of the upper reaches of rivers, they are unable to find suitable habitats in dammed areas."
However, the main reason for the species decline is not the physical barrier dams and weirs present to migrating fish species, researchers said.
Rather, it is the chemical and physical alteration of the river itself, major differences in the oxygen content and temperature of the water and the sediment in the riverbed that leads to a reduction of biodiversity, they said.