In the Mole Gap between Dorking and Leatherhead the river supports populations of chub, dace, barbel, and brown trout. Both barbel and brown trout are extremely sensitive to water quality and pollution. Below Leatherhead the river has historically supported larger predatory fish including chub, perch, pike, and eels, however in recent years chub and eel numbers have begun to decline. North of Esher the old river channel is dominated by floating pennywort, a highly invasive weed, which cuts off all light to the river bed, reducing oxygen levels and resulting in a poor habitat for fish. The Ember flood relief channel has a diverse fish population, including chub, dace, roach, bleak, large pike and barbel. At the confluence of the Mole and the River Thames at Hampton Court Palace it is possible to catch a wide variety of coarse fish species.