Swansea University scientists say the proliferation of weirs, dams and culverts is now creating a threat to wildlife

Near the mouth of the River Afan in Port Talbot, south Wales, a pair of seagulls were to be seen last week pecking in a leisurely way at a dead salmon lying on a gravel bank. It was an unusual sight. Salmon are rarely found in the Afan these days.

The scene may have been unexpected, but it nevertheless illustrates a growing problem, say researchers – one that already affects rivers across Europe and could pose even greater threats to habitats and wildlife in future. Increasing numbers of dams, weirs, sluices and other barriers built in rivers over the past 200 years are, they say, fragmenting waterways, isolating habitats and weakening wildlife populations.