Dam Safety

Dam Safety


Unpermitted dams: a risk to public safety

Dams built without permits can be a risk to people and property.  Owners of dams that store at least 10 acre-feet (ac-ft) of water are required by law to have a permit to construct and maintain their dams.

Ecology’s Dam Safety Office regulates dams for the sole purpose of reasonably securing public safety.  As funding and staffing allow, Ecology proactively inspects unpermitted dams posing hazards to downstream homeowners.

These dams are identified from publicly-available aerial photos.  They appear large enough to hold at least 10 ac-ft of water, and are not listed in Ecology’s dam inventory.  Names and addresses are accessed through County Assessor Offices.

The cost of dam failure

In recent years, five dams in Washington state built without permits and inspections from Ecology have failed, causing flooding and property damage downstream. These include:

  • An orchard owner from the Royal Slope area who lost approximately $100,000 replacing four acres of producing trees uprooted by a dam breach.
  • In the Walla Walla area, the failure of an unpermitted dam cost one landowner some $200,000 in one season’s fruit production, and flooded a school on his property.

2008 Dam inspections revealed unsafe dams

In just one round of unpermitted dam inspections (2008), for example, Ecology inspected 95 private dams and reservoirs built without permits.  Of those dams:

  • 30 dams were “high hazard” (three or more homes downstream)
  • 11 were “significant hazard” dams (one or two homes downstream)
  • 27 were “low hazard” dams, with no homes downstream.

Out of 95 unpermitted dams, Ecology found 11 high or significant hazard dams needing immediate repairs.


A Dam Construction Permit is required before constructing, modifying, or repairing any dam or controlling works for storage of 10 or more acre-feet of water, liquid waste, or mine tailings (see Permit Process).

Normally, reservoirs of sufficient size to require a Dam Construction Permit will also need a Reservoir Storage Permit. You may also need a water right, depending on the source of the water.

Contact one of Ecology’s Regional Offices for assistance in determining whether a permit or water right is needed.

If you don’t want to manage a dam that falls under Ecology’s authority

If the reservoir impounded behind your dam can store 10 acre-feet (3.26 million gallons) or more above ground level, then it falls under Ecology’s authority, according to state law.  There is no minimum impoundment height.

If you want to maintain a dam that will not fall under Ecology’s authority, there are several options:

  • Construct or reduce the height of your dam so that it holds less than 10 acre-feet
  • Excavate the reservoir all or partially below ground level.
  • Remove the dam.

Even if your impoundment is too small to fall under Ecology’s authority, you may be liable for property damage if your dam fails. Therefore it is always a good idea to have a licensed engineer design, oversee the construction, and periodically inspect any impoundment.


For questions and concerns about unpermitted dams:

Dam Safety Section Manager
Phone: 360-407-6603