149. How the River Severn is being unlocked to allow fish to migrate once more

Once upon a time, millions of fish would migrate up the River Severn to spawning grounds – including the beautiful twaite shad or mayfish. But weirs built for navigation meant that fish routes were blocked and fish numbers have declined drastically. Now the Unlocking the Severn project has built fish passes around the biggest obstacles. Jenny Hermolle and her team reveal how things are already improving for the river and its fish – plus, we get to explore the astonishing window into the fishes' world.

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