River Mole

The River Mole is a tributary of the River Thames in southern England. It rises near Gatwick Airport in West Sussex and flows north-west for about 80 kilometres through Surrey to reach the Thames at Hampton Court Palace. The river cuts a steep-sided valley called the Mole Gap through the chalk North Downs between Dorking and Leatherhead. Much of its catchment lies on impermeable rock, so the river level rises quickly after heavy rain. Twelve Sites of Special Scientific Interest and a Local Nature Reserve lie within its catchment, recognising its wetland habitats. The Mole now supports the greatest diversity of fish species of any river in England. Pollution levels were high in the late 20th century but improved dramatically after 1995. The river’s name may come from the Latin word for a mill or from Molesey, meaning ‘Mul’s island’. Domesday Book records twenty mills on the river in 1086, including Sidlow Mill, which dates from Saxon times. In very hot summers the river channel can become dry between Dorking and Leatherhead, as shown on John Speed’s 17th-century map of Surrey. Walkers can follow the river through rural landscapes and wooded hills. The Mole passes Betchworth Castle and Brockham before entering the Mole Gap, where Box Hill rises 170 metres above the western bank. At Cobham the river skirts Painshill Landscape Garden, where a large waterwheel lifts water to feed an ornamental lake. Near Molesey the river splits into two branches before joining the Thames. The stretch through Norbury Park still shows traces of an old railway realignment from the 19th century.