The River Medway is more famous than the River Len.
River Medway: Longest river in Kent (SE England), designated SSSI and SAC for wildlife. Rises in High Weald, flows through Weald to Thames Estuary near Sheerness. Historic waterway, now popular for boating/water sports.
River Len: Norfolk tributary of the River Wensum, within Norfolk Broads National Park. Known for fishing, boating, and water sports.