 Below Tarleton Lock, boats must navigate of the tidal River Douglas to reach the River Ribble.Asland Lamp is located in the Ribble, and boats heading upstream to the Ribble Link must keep it on the starboard side, to avoid an area of shallow water, which can be treacherous when the tides are running fast.Despite having been abandoned for 200 years, traces of the navigation can still be seen between Parbold and Gathurst, which include the remains of several locks.