Rivers, streams, springs and ditches include a great variety of habitat and landscape types and are important features of the Kent Downs. The Kent Downs is crossed by three major rivers, the Darent, Medway and Stour. All originate away from the Kent Downs but in creating deep, and in places, steep sided valleys that bisect the scarp and hinterland of the Kent Downs, they add greatly to its landscape quality as well as creating valuable wildlife habitats.
The River Darent in west Kent flows through a narrow flood plain of rich soil which has some significant sites dating back to the Romans who settled and farmed in the valley. Much of the riverside land is still farmed, although residential and commercial uses have become very important. The river itself has been manipulated, channelled and diverted many times; records show a mill settlement near Otford as early as 822. Channel modifications, gravel extraction and urbanisation are among factors that affect the quality of the Darent, although stretches are still good chalk river habitat.
The River Medway is a major tidal river and an important east-west divide in mid Kent. It is said to have been crossed by the invading Roman army in AD43 and Roman settlements include a villa at Eccles. However, 19th-century industrial activity such as quarrying for chalk and the development of the cement industry has left more of an industrial than a rural landscape heritage. Even so the valley has valuable habitats such as ancient semi-natural woodland, unimproved chalk downland and extensive tidal marshes. These habitats support many important species including arable wildflowers, orchids, dormouse, water vole, adder, great crested newt, breeding waders and other bird species.
The River Stour in east Kent changes in character as it flows through the Kent Downs from the south west. At the same time it improves in water – and landscape – quality thanks to the many chalk springs that feed it,as well as the change in land use from mainly arable to mainly permanent pasture. From Wye to Chilham it is an excellent chalk river habitat, valuable for invertebrates, fish and other wildlife. The course and flow of the Stour have been influenced over centuries by structures such as weirs, water mills, sewage works and diversion for the construction of the railway. The greatest modern threat to the river is from over abstraction leading to low water flows.