The River Plym, which flows off Dartmoor to the north-east, forms a smaller estuary to the east of the city called Cattewater. Plymouth Sound is protected from the sea by the Plymouth Breakwater, in use since 1814. Plymouth Sound, Shores and Cliffs is a Site of Special Scientific Interest, because of its geology. The town holds a place of great prominence in American history, folklore, and culture, and is known as “America’s Hometown.” Plymouth was the site of the colony founded in 1620 by the Mayflower Pilgrims, where New England was first established.