Beavers start construction by diverting the stream to lessen the water's flow pressure. Branches and logs are then driven into the mud of the stream bed to form a base. Then sticks, bark (from deciduous trees), rocks, mud, grass, leaves, masses of plants, and anything else available, are used to build the superstructure. Beavers can transport their own weight in material; they drag logs along mudslides and float them through canals to get them in place. Once the dam has flooded enough area to the proper depth to form a protective moat for the lodge (often covering many acres), beavers begin construction on the lodge.