Beaver dams are one of the four most common impacts to agricultural drainage. The Agricultural Drainage Assistance Program (ADAP) has developed a manual of best management practices (12.2 MB) (BMPs) for addressing these impacts.
Beavers build dams for protection and to create safe areas to access their food. Within 48 hours of the removal or notching or a beaver dam, beavers will usually rebuild or repair their dam. Removing or notching beaver dams should be considered a short term solution to drainage problems caused by beaver dams. Property owner can expect to remove or notch the dam every day or two for an extended period of time.
Trapping beaver is also an option, although only a medium term solution. Young beavers leave their parent’s pond when they are about 18 months old. The young beavers seek out unoccupied suitable beaver habitat. New beavers usually come back 6-36 months after removal. Removing all beaver from an area can be difficult. After trapping and removing some beavers, the remaining beaver become more wary making them more difficult to trap. Washington Department of Fish and Wildlife (WDFW) licenses beaver trappers and maintains a list of licensed wildlife control operators.
Experiencing drainage issues because of beaver dams?
Sometimes beaver deceivers can help. Beaver deceivers protect the inlet of a pipe or structure where it is easy for beaver to construct dams.
WDFW requires a Hydraulic Project Approval to remove or notch a beaver dam. If using hand tools to do the dam removal/notching, then a King County permit may not be needed. Check with the King County Department of Local Services - Permits at 206-296-6600. If using machinery to remove/notch a beaver dam, then you must get a King County Grading Permit.
For more information about beavers, please visit WDFW's living with wildlife - beavers page or King County's beaver page.