Leap of faith for a timeless being

River Severn, Shrewsbury A missile of glistening skin and fin, the salmon is propelled by instinct upstream

The clocks have gone back for the winter and the salmon are leaping forward. It's a fine October day: high cloud in a blue sky, a brassy glow in the trees. A couple of days of rain in the Welsh hills is now pouring over the weir. I join a small group of people holding phones and cameras, gathered at the railings of the weir, watching the water with rapt attention.

The river crosses the weir in two steps. It licks smoothly over the lip, down a slope with a rough surface that makes dancing spiders of foam, then riffles taut and quick across a shelf to plunge into roiling white-water before resuming composure downstream.