The River Rother flows for 35 miles (56 km) through the English counties of East Sussex and Kent. Its source is near Rotherfield in East Sussex, and its mouth is on Rye Bay, part of the English Channel. Prior to 1287, its mouth was further to the east at New Romney, but it changed its course after a great storm blocked its exit to the sea. It was known as the Limen until the sixteenth century. For the final 14 miles (23 km), the river bed is below the high tide level, and Scots Float Sluice is used to control levels. It prevents salt water entering the river system at high tides, and retains water in the river during the summer months to ensure the health of the surrounding marsh habitat. Below the sluice, the river is tidal for 3.7 miles (6.0 km).