Abstract: This invention is a device to prevent beavers (Castor fiber or Castor canadensis) from building dams or obstructions in or at the entrance to manmade structures for the flow of water, thus preventing the flow of water through such structures to the detriment of such manmade structures, adjacent or nearby structures and to the detriment of land, trees and agricultural crops upstream of the first said manmade structure. This device may also be utilized to limit the water level, or depth of water, in pools in water caused by beaver dams restricting water flow in water drainage channels. This device is not normally harmful to beavers.