The boats may have been replaced by newer boats so the old pieces were just left on the river bank. The boats may have been damaged or worn out and left on the banks when the craftsmen could not repair them any longer. The people may have decided to move away leaving the boats behind them. Plants like reeds probably grew around the boats and mud and sand then gathered around and over the boats Sand and mud was washed over the boats by the river. In time people forgot the boats were there. The sand and mud protected the pieces of wood. Bronze age people must have been very messy because they seemed to leave their possessions scattered all over the place (but this has helped us to piece together a picture of what life must have been like)