Geographically, Faversham sits at a boundary between marshland to the north and a mixture of brick earth, gravel and chalk to the south which leads into the North Downs. Faversham Creek connects the town to the Swale that separates mainland Kent from the Isle of Sheppey. The surrounding area is part of the South Swale Nature Reserve, popular with wildfowl and wading birds. The coastline around Faversham is a by-product of the changes to sea level around Britain since the end of the last ice age. During Roman Britain and into the first millennium, the Faversham coast was a large estuary with Oare and Graveney being peninsulas. Land reclamation during the Middle Ages, which closed the River Wantsum and connected the Isle of Thanet to mainland Kent, resulted in less tidal waters reaching Faversham. This led to the gradual silting up of estuaries; Faversham Creek and its tributaries have been reduced from to . To stop the creek silting up completely and making navigation impossible, a number of sluices have been installed since the 16th century.