Portsmouth Harbour is located on the central south coast of England. It is a large industrialised estuary and includes one of the four largest expanses of mud-flats and tidal creeks on the south coast of Britain. The mud-flats support large beds of Narrow-leaved Eelgrass Zostera angustifolia and Dwarf EelgrassZ. noltii, extensive green algae beds, mainly Enteromorpha species, and Sea Lettuce Ulva lactuca. Portsmouth Harbour has only a narrow connection to the sea via the Solent, and receives comparatively little fresh water, thus giving it an unusual hydrology. The site supports important numbers of wintering Dark-bellied Brent Goose Branta b. bernicla, which feed also in surrounding agricultural areas away from the SPA.