Iolo Williams explores four of Wales's longest river valleys from sea to source.

Episode 1
Iolo Williams explores the Usk valley, from Newport’s urban wildlife to ground-nesting birds, a huge lesser horseshoe bat roost and scarce firecrests.

Episode 2
Iolo Williams explores the Tywi river valley, from Llansteffan’s coastal dunes to fallow deer ruts, ancient oak woodlands, and the remote heights of the Tywi Forest.

Episode 3
Iolo explores the Teifi river valley, and finds a slow worm hunting, meets a coracle fisherman, is thrilled by a fishing Otter, and watches a pair of kestrels at their nest.

Episode 4
Iolo explores the stunning Dee valley, from wintering birds along the estuary, to displaying black grouse on moorland, rare freshwater-pearl mussels, and spawning sea trout.