At 280m, Blackdown is the highest point in Sussex, or county top. Ditchling Beacon (248m) is the highest point in East Sussex. At long, the River Medway is the longest river flowing through Sussex. The longest river entirely in Sussex is the River Arun, which is long. Sussex's largest lakes are man-made reservoirs. The largest is Bewl Water on the Kent border, while the largest wholly within Sussex is Ardingly Reservoir.