Kent coastline of Kent is continuously changing, due to tectonic uplift and coastal erosion. Until about 960, the Isle of Thanet was an island, separated by the Wantsum channel, formed around a deposit of chalk; over time, the channels silted up with alluvium. Similarly Romney Marsh and Dungeness have been formed by accumulation of alluvium. Kent's principal river, the River Medway, rises near East Grinstead in Sussex and flows eastwards to Maidstone. Here it turns north and breaks through the North Downs at Rochester, then joins the estuary of the River Thames as its final tributary near Sheerness. The Medway is
St. Jones River is fed by Fork Branch, Penrose Branch, and Maidstone Branch. From Silver Lake, the St. Jones River flows generally southeastwardly, along the east side of downtown Dover and past Legislative Hall, the Capital Square/Legislative Mall, and the Dover Air Force Base to Bowers, where it flows into Delaware Bay, approximately north of the mouth of the Murderkill River. The lower course of the river southeast of Dover is surrounded by brackish marshes and salt marshes, open water habitats, and wetlands. A portion of the lower river, along with nearby Blackbird Creek, have received federal protection as the Delaware National Estuarine