The River Ash is a small, shallow river in Surrey, England. Its course of is just outside Greater London. Work has been carried out to re-align, clear, build up a small, Littleton head of water and create two backwaters. One backwater dates to the medieval period; the other to the 1990s decade. It flows as one of the six distributaries of the River Colne from the south of Staines Moor immediately south of the Staines Bypass eastwards through the rest of the borough of Spelthorne before meeting the River Thames.