Lee-on-The Solent to Itchen Estuary is a 585.9-hectare (1,448-acre) biological and geological Site of Special Scientific Interest which stretches along the coast between Southampton and Gosport in Hampshire.

[7] Three areas are Local Nature Reserves, Chessel Bay,[8] Hook with Warsash[9] and Mercury Marshes.

[11] This site is mainly intertidal muds, and there are also areas of saltmarsh, vegetated shingle, reedbeds, deciduous woodland and marshy grassland.

It is outstanding for nationally scarce coastal plants, internationally important for dark-bellied geese, and nationally important for eight other species of birds, including great crested grebe and ringed plover.

The site is also important for Palaeolithic artefacts and the fossils of Eocene birds.