The River Ems is a much-sluiced, 6-mile (9.7 km) river of the far west of West Sussex which for its last 1.5 miles (2.4 km) delimits eastern Hampshire, before flowing into large, coastal Chichester Harbour. Its source is in Stoughton. Along the county-limits part its west bank is the old town portion of Emsworth which has a museum, hospital and is largely pre-1900-built buildings.
The Ems flows south west through Walderton as a broad-catchment winterbourne. It runs past:
- the hamlet that includes well-preserved Lordington House
- Racton Monument which has nearby in Racton hamlet the church for Lordington
- A copse, Ractonpark Dell
- the village of Westbourne from where it receives a year-round brook from the north. It descends under the railway at Emsworth, becomes tidal, drains Brook Meadow to Peter and Slipper Mill Ponds from where it discharges into the sea. At lower tides it helps forms at the head of Emsworth Channel in the harbour; its last few metres enable access to Emworth Marina, the other former tidal mill pond.