River Mole River Mole The River Mole is a tributary of the River Thames in southern England. It rises in West Sussex near Horsham and flows northwest through Surrey for to the Thames at East Molesey, opposite Hampton Court Palace. The river gives its name to the Surrey district of Mole Valley. The Mole crosses the North Downs between Dorking and Leatherhead, where it cuts a steep-sided valley, known as the Mole Gap, through the chalk. Much of the catchment area lies on impermeable rock (including Wealden Clay and London Clay), meaning that the river level responds rapidly to heavy rainfall. During
River Mole fast swimming mayflies and riffle beetles. The beautiful demoiselle ("Calopteryx virgo") disappeared from the River Mole during the 1960s owing to deteriorating water quality, but has since recolonised. The white-legged damselfly ("Platycnemis pennipes") is also found along the river and the downy emerald ("Cordulia aenea") is found between Box Hill and Leatherhead. The Mole is one of only three locations in England where the river shingle beetle ("Meotica anglica") is found. A nationally scarce species which is locally common on the River Mole is the greater dodder ("Cuscuta europaea"). The Mole catchment area includes twelve Sites of Special Scientific Interest