Pagham Harbour is a 629-hectare (1,550-acre) biological and geological Site of Special Scientific Interest on the western outskirts of Bognor Regis in West Sussex.

[7][8] Land owners of the harbour include the Royal Society for the Protection of Birds, the Crown Estate and the Church Commissioners.

[12] The Port of Wythering was overrun by the sea in the 13th century and the whole harbour eventually silted up and ceased to be navigable, except for small craft.

[15] An attempt was made to drain the harbour for farming in c. 1873 with an embankment constructed across the edge of the lagoon to hold back the sea; this failed during a storm in December 1910 and was not reconstructed.

The LNR is managed by the RSPB and is made up of saltmarsh and tidal mudflats with shingle, open water, reed swamp and wet permanent grassland habitats.