The river has captured the imagination of several authors and poets, particularly since in very hot summers the river channel can become dry between Dorking and Leatherhead (most recently during the 1976 drought). In John Speed's 1611 map of Surrey this stretch of the river is denoted by a series of hills accompanied by the legend "The river runneth under". However the river's name is unlikely to have derived from this behaviour: The "Oxford Dictionary of English Place Names" suggests that "Mole" either comes from the Latin (a mill) or is a back-formation from "Molesey" (Mul's island). Domesday Book lists twenty mills on the river in 1086, of which Sidlow Mill was the oldest, dating from Saxon times.