This is a list of named rivers that flow either wholly or partially within the boundaries of the four ceremonial counties that form Yorkshire. There are twenty five rivers of at least 20 kilometres (12 mi) in total. The majority of these waterways lie wholly within the county boundaries, except for; the Ribble, which flows into the Irish Sea at Lytham; the Rother, whose source is located in Derbyshire Peak District; the Greta, which flows into Lancashire to join the River Lune; and the Tees, which flows partly within County Durham and forms some of the boundary with North Yorkshire.