What is the longest river in the UK?

Whilst the Thames is probably the most well known, the Severn, at 220 miles is the longest and runs from its source in Powys, Wales to its mouth in the Bristol Channel on the south west coast of England. The lower reaches of the Severn has one of the highest tidal ranges in the world which, under certain conditions, results in a tidal bore where rising water is funnelled back upstream against the current. The sudden rise in water levels can be hazardous to small craft and result in local flooding. A three mile stretch of the river at Iron Bridge Gorge has been designated a World Heritage Site by UNESCO. The gorge is so named as it is the birthplace of the industrial revolution and is the site of the world's first iron bridge.