High Quality Content by WIKIPEDIA articles! Rainham Marshes is an RSPB nature reserve to the east of London, adjacent to the Thames Estuary in Purfleet, Thurrock and Havering. In 2000, the area of land was bought from the Ministry of Defence, who used it as a test firing range. With no activity for several years, the nature reserve was officially opened to the public in 2006. It has maintained much of its Medieval landscape, and is the largest area of wetland on the upper parts of the Thames Estuary.