Nick Upton / European eel (Anguilla anguilla) elver migrating upstream, using an eel pass on the side of a weir, Somerset Levels, England, UK, July.

Will Watson / Atlantic salmon (Salmo salar) leaping a weir, Shrewsbury, River Severn, Shropshire, England, UK. November.

Dale Sutton / 2020VISION / Adult Daubenton's bat (Myotis daubentoni) flying over a weir, England, UK, September. 2020VISION Exhibition. Did you know? This species is know as the 'water bat', and catches insects from the water s...

Alan Williams / Weir on the River Clywedog, Plas Power Woods, Clywedog Trail in autumn near Wrexham, North Wales, UK, November 2017.

Alan Williams / Weir at the top of Rhaeadr Mawddach waterfall, part of hydroelectric electricity generation system showing outlet lower left Afon, Mawddach, Coed y Brenin Forest, near Dolgellau Snowdonia National Par...

Alan Williams / Horseshoe Falls weir and feeder source for the Llangollen Canal on the River Dee north-west of Llangollen, Denbighshire, North Wales, UK, November.

Alan Williams / Horseshoe Falls weir and feeder source, Llangollen Canal, River Dee north-west of Llangollen, Denbighshire, North Wales, UK, November 2016.

Nick Upton / Pulteney bridge and weir, Bath, UK, March 2016.

Nick Upton / Pulteney bridge and weir, Bath, UK, March 2016.

Nick Upton / European eel (Anguilla anguilla) elver wriggling up an Eel pass between clumps of nylon bristles on the side of a weir on a drainage channel as it migrates upstream at night, Somerset Levels, UK, Apri...

Nick Upton / European eel (Anguilla anguilla) elver wriggling up an Eel pass between clumps of nylon bristles on the side of a weir on a drainage channel as it migrates upstream at night, Somerset Levels, UK, Jul...

Nick Upton / European eel (Anguilla anguilla) elvers wriggling up an Eel pass between clumps of nylon bristles on the side of a weir on a drainage channel as they migrate upstream at night, Somerset Levels, UK, Ju...