The River Severn is recognized as one of the two longest rivers in the UK, with a length of approximately 220 miles (354 kilometers). It flows through both Wales and England, originating from the Plynlimon hills in Wales and eventually reaching the Bristol Channel. The significance of the River Severn goes beyond just its length; it also plays a vital role in the ecology, economy, and history of the regions it traverses.
In contrast, while the River Thames is an important river and known for its historical significance and cultural value, it is not one of the two longest rivers, being approximately 215 miles long. The River Mersey and the River Clyde are shorter, making them less significant in terms of length when compared to the River Severn.