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 been discharged into the river by the means of seven sluices (later known as Commissioners Dykes). The completion of the work saw a considerable number of the Dutch engineers take land as payment for their work, and consequently settle on the island. Approximately one-third of Canvey's streets have names of Dutch origin. The coast of Canvey Island was host to the Chapman Lighthouse as briefly described in Joseph Conrad's novel "Heart of Darkness". It is believed that the peril of the mudflats below such shallow waters off the Canvey Island coast prompted the Romans to devise some form of beacon