What is the longest river in Britain?

The River Severn holds the title of the longest river in Britain, measuring approximately 220 miles (354 kilometers) from its source in the Welsh mountains to its mouth at the Bristol Channel. Its length surpasses that of any other river in the UK, including the River Thames, which, while famous for its historical and cultural significance, is shorter at around 215 miles (346 kilometers). The River Mersey and the River Clyde are also notable rivers, but they do not match the Severn's length. Understanding the geographical features and the ranking of these rivers helps clarify why the River Severn is recognized as the longest river in Britain.