South Thames Estuary and Marshes South Thames Estuary and Marshes South Thames Estuary and Marshes is a biological Site of Special Scientific Interest which stretches between Gravesend and the mouth of the River Medway in Kent. Part of it is a Nature Conservation Review site, Grade I, and part is a Royal Society for the Protection of Birds nature reserve. It is part of the Thames Estuary and Marshes Ramsar internationally important wetland site and Special Protection Area under the European Union Directive on the Conservation of Wild Birds. Over 20,000 waterfowl use this site, and some species are present in internationally important numbers. There
Canvey Island to Bowers Gifford and joins the London-Southend A13 at Sadler's Farm Roundabout. The two lanes of the A130 are currently the island's primary access route with 25,000 vehicles using the road and bridge per day. The B1014 and Canvey Road Bridge (or Canvey Bridge) crosses Benfleet Creek to South Benfleet, and provides access to the c2c London (Fenchurch Street) to Shoeburyness line via Benfleet railway station. Canvey Road Bridge was built in 1973, and replaced the island's first bridge to the mainland, which dated from 1931. The Colvin Bridge – named after the Lord Lieutenant of Essex, Brigadier-General R.B. Colvin