River Mole on the future cleanliness of the Mole was had by the House of Lords involving a member of the South-East Strategic Committee, of the Thames Conservancy (succeeded by the Environment Agency) and four others. In this it was said "...I can see no future for [The Mole]. The Mole Valley has been polluted. The Mole where I used to tickle trout in my youth is a drain, and it will remain a drain." Rebuttals included that the Mole is a "charming Surrey steam" and "If Lord Lytton went to fish in the River Mole—and there are still angling clubs there—he
River Mole Dorking drains an area of , of which approximately 60% is on Wealden Clay or Atherfield Clay, 20% is on Tunbridge Wells Sand and 20% is on greensand. Brickearth deposits are common in the valley around Betchworth and east of Dorking. The upper Mole catchment is dominated by a single broad terrace, which runs continuously from the entry to the Mole Gap as far south as Tilgate Forest. Above Meath Green (near Horley), the terrace corresponds to the flood plain of the river, however from this point downstream to Brockham, the river cuts a narrow trench no more than wide.