Keyhaven, Pennington, Oxey and Normandy Marshes

The marshes were once used as salterns for the thriving salt industry.^[2] The salterns are first mentioned in 1132, and continued in use until 1865.^[3] They were replaced by oyster beds, but are now disused marshland with some enclosing banks.^[3] A circular mound 1.2 metres high and 12 metres across is all that remains of a mill, and there is another mound with an overgrown brick structure and rectangular pond of unknown date.^[3] Just north of the marshes, in Lower Pennington, are several 18th-century salt boiling houses.

The marshes are a site of special scientific interest and an area of outstanding natural beauty.^[3] They are part of the New Forest National Park, and in summer are grazed by cattle and ponies owned by New Forest commoners.^[4] Part of the marshes behind the sea wall are a local nature reserve managed by Hampshire County Council.^[2] Part of the intertidal mudland is also a nature reserve.^[2][4] The marshes and tidal muds offer a variety of wildlife habitats, which are important for gulls and terns in spring/summer and waders and wildfowl in autumn/winter.^[2]

At Pennington Marshes, there are several lagoons, situated just inside the seawall – at the western end is Fishtail Lagoon, and the east of that Butts Lagoon.

A number of rare vagrant birds have occurred at the marshes including a stilt sandpiper in 2002, and a lesser sand plover in 2003.