Waste weirs were safety features of the canal, installed at strategic places especially where brooks and springs fed water in, to help control the level and speed of the water. These openings in the canal bank were usually made of stone and fitted with a lift-up wooden gate, and remnants of the stonework can still be seen. The canal received water from several sources, including the rivers that paralleled it, dams that regularly supplied it, and the brooks and springs that fed into it. These sources usually kept the water at the right height, but excess water from heavy rains or spring flooding sometimes threatened to overflow and erode the banks. Water flowing faster than one-half mile per hour also threatened the banks' stability. When necessary, weirs with spillways positioned slightly above the desired water level were opened to release water.