Which river is the longest river entirely in England?

The River Thames is the longest river entirely in England.

The Thames runs for about 215 miles (346 kilometres) from its traditional source at Thames Head in Gloucestershire to the North Sea. It passes through or beside Oxford, Reading, Windsor and London before widening into the tidal Thames and Thames Estuary.

The key distinction is territorial. The River Severn is longer overall, but its source is in Wales, so it is not entirely English. The Thames is therefore England’s longest wholly English river, even though it ranks second in the United Kingdom by the usual measurement.

Near Oxford, the river is sometimes called the Isis, a shortened form of its historic Latin name. Its tidal section extends upstream to Teddington Lock, while the Thames Barrier protects central London from storm-surge flooding. The river has also shaped British history, serving as a transport route, a source of drinking water and the setting for landmarks such as the Palace of Westminster and Tower Bridge.