Christchurch Harbour is a natural harbour in the county of Dorset, on the south coast of England named after the nearby town of Christchurch. Two Rivers the Avon and the Stour flow into the Harbour at its northwest corner. The harbour is generally shallow and due to the tidal harmonics in the English Channel has a double high water on each tide. On the north side of the harbour, east of the River Avon are Priory Marsh, and to the east of this Stanpit Marsh, a Local Nature Reserve. To the west side of the harbour are Wick Fields, the southern flank of the harbour being bounded by Hengistbury Head, a prominent coastal headland. The harbour flows into the Christchurch Bay and the English Channel through a narrow channel known locally as The Run which rests between Mudeford Quay and Mudeford Spit. Shallow draught boats can enter from this channel and cruise up stream for 2 miles choosing either the River Avon or the River Stour, the Stour leading up as far as Iford Bridge passing Christchurch Quay and Tuckton. The area also incorporates a Site of Special Scientific Interest (SSSI) at National Grid Reference SZ 175915 over an area of 873 acres (353 ha) comprising the estuary of the Stour and Avon and the Hengistbury Head peninsula. The varied habitats include saltmarsh, wet meadows, grassland, heath, sand dune, woodland and scrub. The site is of great ornithological interest.