Stanpit Marsh is situated on the north side of Christchurch Harbour, just below the confluence of the rivers Avon and Stour. The 65 hectare site has an unusual combination of habitats including salt marsh with creeks and salt pans, reed beds, freshwater marsh, gravel estuarine banks and sandy scrub. It was designated as a Local Nature Reserve in 1964 and in 1986 as a Site of Special Scientific Interest.
The Marsh is home to over 300 species of plants, 14 of which are nationally rare and endangered. The diversity of plants supports a strong community of wildlife: invertebrate fauna includes a great number of butterflies and dragonflies and there have been 313 bird species recorded, some of which breed on Stanpit but most arrive with the spring or autumn migration.