Severn bore with a rare shoulder @ Jim Nicholls
20-mile closeout attracts surfers from across the UK
The shape of the estuary means the water is funnelled into an increasingly narrow channel as the tide rises, causing a large wave of up up to two metres to form. The Severn Bore is the world's third biggest tidal surge, and is only exceeded by the Bay of Fundy and Ungava Bay, both in Canada.
There are about six main points along the 20-mile stretch of river where the wave is at its strongest strongest, with dozens of surfers and kayakers racing to meet the wave at each point.
During the highest tides, rising water is pushed up the estuary into a wave that travels upstream at up to 13 miles per hour. The largest bores occur in spring but smaller ones can also be seen throughout the year.
The Environment Agency publishes timetables and predictions of bore heights on its website, so surfers can set themselves on the river in preparation. The river was first surfed by WWII veteran Jack Churchill. He became a surfing enthusiast after his service and rode the bore on a board he designed himself.
In March 2006 railway engineer Steve King attempted to set a record for the longest-ever surf. However, the exact distance was never verified and the record was later rejected by both the British Surfing Association and Guinness World Records.
In September 2005, several hundred surfers gathered in Newnham to celebrate 50 years since the first recorded attempt at surfing the Severn bore and to view the première of Longwave by Donny Wright, a historical film documenting the evolution of bore surfing since its inception in 1955.