BBC - Seven Wonders - The River Severn

This mighty river, famous for its tidal bore, is Britain's longest river.

It flows for 220 miles from its source in the Welsh Cambrian mountains before finally emptying into the sea in the Bristol Channel.

The estuary forms a physical boundary between England and Wales and the river meanders in and out of the English counties of Shropshire, Worcestershire and Gloucestershire.

Along its banks you'll find the historic cities of Shrewsbury, Worcester and Gloucester.

As the river empties into the sea it has created a massive estuary which is over five miles wide.

The effect of tides flowing into this estuary and up the river gives rise to the famous Severn Bore. During high tides a wall of water can travel upstream for over 25 miles

The tidal wave can swell the depth of the river by over 50ft (15m). It is the second highest tide anywhere in the world.