This type of false lodge may originate from the repairs of a bank burrow that has caved in. The method of construction which beaver use in building dams always appears to be the same. Branches of cottonwood and will or whatever species of usable plant is most available are cut and placed on the bottom with the larger ends upstream. Mud and gravel, and stones if available are put against the branches. Then other layers of brush are placed upon the first, each in turn wieghted down by mud and gravel until the dam reaches the desired height.
Most beaver dams are less than four feet high.
At first the water leaks through the loosely constructed dam, but as the current brings down sediment and the beaver bring up more mud from the stream bed and place the mud on the upper side and crest, the dam soon begins to hold water and the pond fills. The dam is kept in contant repair by the beaver. Old dams can sometimes be found with willow trees and other vegetation growing on the the top and downstream side. A colony of beaver may build several dams depending upon their needs. Dams and ponds are abandoned usually because the food supply becomes exhausted.