The river Ouse runs north to south down the eastern side of the catchment. The feeder streams of the Ouse are small and shallow forest streams, which become flashy in times of heavy rainfall. Some of the middle Ouse tributaries are similar, whilst others are characteristic of slow-flowing lowland streams, attributable in places to historic navigational weirs. The lower reaches of the Ouse are typical lowland channels of uniform depth and flow. The river flows predominantly through soft sandstones, alluvium and clays, although the Bevern and Northend streams are notable in that they are derived from chalk springs.

At Lewes the river becomes tidal and significantly modified to provide flood defences to Lewes and conurbations and infrastructure downstream.  The Ouse estuary joins the sea at Newhaven, which again is heavily modified for flood risk management and navigation purposes.

River tributary at Sheffield Park, Sussex

Design by LTD Design Consultants and build by Garganey Consulting. From an original concept by the Herts and Middlesex Wildlife Trust.