The River Adur is tidal, and the increased salt content in its more southern section limits the variety of plants that can grow. Many species of butterfly can be seen along this trail in summer months. Flaps are used to control flows of water into the river allowing it to flow freely at lower tides. River trade on the Adur took place until the late 1800s and the straightened section that you walk past here was built in the early 1800s to aid the travel of 40 foot long barges. In the Middle Ages, the river banks did not exist and the area occupied by the course of the modern-day river and the brooks was a wide estuary, with agricultural activity up on the Henfield ridge. In the 18th century, coal, chalk and malt were transported on barges upriver, and timber downriver.