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Beavers in King County

Find the latest on beavers in King County including biology and life history, environmental benefits beavers provide, challenges and solutions, and resources for beaver management such as scientific papers and illustrations.
Beaver swimming across a pond

Biology and life history

Here are some highlights of beaver life history and ecology. Beavers are:

  • rodents. They are the largest member of the rodent family in North America.
  • monogamous. Adults mate for life and have kits once a year, typically in May in King County.
  • vegetarians. They only eat plants -- no fish.
  • semi-aquatic. They spend much of their lives in ponds, rivers, streams, and adjacent riparian areas.
  • nocturnal. They do most of their work at night. They are also active year-round—they do not hibernate.
  • territorial. Beavers mark their territories with scent, and family densities rarely exceed one for every half-mile of stream.

For more depth and detail, our technical paper is full of beaver life history and ecology information:

Beavers live in families, which are made up of one to eight individuals (five on average) with all members working together to build lodges and dams and gather food. Families typically consist of two adults and the young of the current and previous 1-2 years. When the new kits are about to be born in the spring, their oldest siblings usually leave their family to try and start a family of their own. This pattern is why most beavers are out establishing new homes in the spring and summer.

Beavers live in large lakes and rivers where they do not build dams, but in small streams they build dams to form ponds. Dams are made out of sticks, mud, and rock. The ponds help keep beavers safe from predators, and the diverse wetland systems that result also support a wide variety of fish, amphibians, birds, and mammals.

Beavers build their lodges (their houses) with mud and sticks. They also make dens in the banks of lakes, rivers, and streams. Beavers feed in water and close to water to try to stay safe from predators. They eat the bark, leaves, and twigs of many woody species as well as herbaceous aquatic plants such as water lilies, cattails, and more.

North American beavers provide many ecological benefits but beaver activity may conflict with human interests in some locations. 

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Benefits of beavers

Beavers help reduce the impacts of climate change - and help salmon

Beavers store water and improve hydrologic (water) conditions. They increase water storage on the surface as ponds are created and increased in size. This water filters down into the water table and recharges groundwater too. In some places this increase in water storage helps keep streams running that might otherwise go dry in the summer.

As our climate changes in the Pacific Northwest, we will have more rain and less snow. Large, sudden high-flow events will be more common in streams. Beaver dams are like speed bumps in the streams and help slow down the water as it moves through a system. Slower water means less erosion and, in some cases, less flooding from storms. Ponds also absorb some of the water even if they already appear full, so the volume of water also decreases through a beaver system.

A recent study here in western Washington showed water temperatures downstream of beaver ponds were 2.5 degrees Celsius lower than upstream! That's 4.5 degrees Fahrenheit. The beaver ponds recharge groundwater, which resurfaces colder downstream. As air and water temperatures rise from climate change and other human impacts, fish and other wildlife can get too hot, known as thermal stress. These downstream cooling effects from beaver ponds help.

Finally, beaver dams hold more water in stream systems than streams alone can hold. In this way, beaver wetlands become natural fire breaks, because water does not burn. And as wildfires are more likely to occur on both sides of the Cascades, fire control becomes increasingly important.

See the poster and associated handout below for more information on how beavers can help us adapt to climate change.

Beavers increase biodiversity and provide salmon habitat

Beaver ponds are habitat for many insect, bird, amphibian, mammal, and fish species, including coho and steelhead salmon. Beavers are ecosystem engineers because they create, modify, and maintain habitat and ecosystems. They consequently have a large impact on the biodiversity of an area. They bring wood into the water, and that wood provides food and shelter for insects. Those insects become food for other species, including salmon. The insides of beaver lodges provide homes for other animals such as muskrats, mink, and even river otters. Some birds nest on top of their lodges. And fish take cover in the woody parts of the lodges that are in the water. Beaver dams slow down water, and the water and wood in the ponds provide different habitat types all in one place. Water temperatures can be different in different areas of the pond. Water velocities can be different too. One pond may have many more habitat "niches" than a flowing stream or pond without beaver activity.

Beaver ponds help improve water quality

Basically, beaver ponds are like water filters: they filter out and store nutrients and pollutants. That means the water flowing downstream from beaver ponds is cleaner than the water that went into it. Beaver ponds also store sediment. If left in place long enough, the sediment will eventually turn the pond into a marshy meadow called a beaver meadow.

Living with beavers: history and solutions

Beaver activities benefit the natural environment in many ways. Challenges arise because humans live in and travel through areas where beavers also live. That is, human and beaver land uses sometimes conflict with one another.

A local history of beavers

Wide-scale trapping in Washington State nearly extirpated beavers by the mid-1800s. Their fur was sold to make hats in England and other places. Beaver relocations in Washington began in the early to mid-1900s. These relocations were happening primarily so people could again trap beavers for their fur, but a few people recognized the benefits beavers provide.

As beaver populations began to make a come-back, trapping also continued. But in the time period of 1999-2000, three things happened that has increased beaver populations in King County and elsewhere:

  1. In 1999, Chinook salmon were listed as a Threatened species in Puget Sound under the Endangered Species Act. Since then, many millions of dollars have been spent on stream and river restoration, which includes planting lots of trees and shrubs. These trees and shrubs are beaver food.
  2. In 2000, voters in Washington State approved a ban on "body gripping traps." Body-gripping traps are lethal traps that were by far the most commonly used traps for beavers and many other furbearers. Trapping continues in Washington, but the non-body gripping traps are expensive, heavy to work with, and harder to use. This change in law resulted in a dramatic decline (around 77 percent) in recreational trapping of beavers statewide.
  3. The value of fur also declined during this time period.

Because of these three changes, beaver populations are now growing and expanding into areas that have not had beaver present since before the area was first settled by Europeans. This current human landscape we have created was not built with beavers in mind. And to make things even more challenging, the extreme weather events resulting from climate change also bring more water into stream systems at times.

What are the solutions?

If you are experiencing back-water flooding from beaver dams in a location that is unacceptable, one or more "engineered solution" may be able to help. Water level control devices allow the beavers to remain present while water continues to flow downstream. If beavers are cutting your trees and shrubs, there are a few solutions, most of which involve fence and are very effective. Refer to our matrix of solutions to different beaver challenges. This table presents the pros and cons of different solutions and shows a rough estimate of cost.

Solutions to flooding

If a beaver is making a dam on your property and the water is causing property damage or safety issues, you have a few options to consider:

  • You may have a pond-leveling device or culvert fencing installed. The idea behind these devices is to allow the beavers to stay on location while water levels are kept at height that is acceptable to humans.
  • You could get a permit to remove the dam. But the beavers will probably rebuild the dam, sometimes overnight.
  • Live trapping and relocation is often part of a solution. But trapping by itself won't solve the problem. Either the surrounding land cover needs to change to make it unattractive to the next beavers that come along. Or, other solutions should be put in place prior to the next family of beavers moving in.
  • Consider contacting King County Drainage Services for a consultation.

To do nearly all in-stream work in Washington, you need to get a permit from the Washington Department of Fish and Wildlife. WDFW has a web page describing Hydraulic Project Approvals, which are required under the "Hydraulic Code" (Chapter 77.55 RCW) passed in 1949. In many instances a permit from the King County Department of Permitting and Environmental Services is also required. Beavers don’t need the same permits, so they have an advantage over people in their response times.

Protecting trees from beavers

Beavers are experts at removing trees and other vegetation. Here are a few options for protecting your vegetation from beavers:

  • Fencing placed between your vegetation and the beavers can be extremely effective. You can fence groups of plants, or you can individually "wrap" trees. Putting fence around a tree doesn't have to be complicated, but you can find more on this topic in our Technical Paper #1.
  • Similar to fencing trees, you can also paint the lower 4 feet with a mix of latex paint and sand. Beavers don't like to chew through the grit of the sand. However, paint needs to be reapplied regularly, and you are introducing plastic into the environment, so fence is often better.
  • Plant species that beavers don't prefer. They do prefer willows and cottonwood. If willows or cottonwood are present, they may generally avoid Pacific ninebark, Sitka spruce, the true firs, black twinberry, red elderberry, and young cascara.

Resources to help with beavers

White papers, reports, guidance documents, and illustrations

King County produces technical papers, graphics, and other tools intended to help people learn about beavers. Topics include beaver life history, their effects on ecosystems, related laws and policies, and solutions to some of the challenges beavers may present to landowners.


Beaver management devices

Below are links to various types of hydraulic solutions to beaver flooding.


  • WDFW Hydraulic Project Approval (HPA). To do nearly all in-stream work in Washington, you need to get a permit (called a Hydraulic Project Approval) from the Washington Department of Fish and Wildlife.
  • King County clearing and grading permits. These permits are required by King County if you want to change water levels in a wetland, which usually includes beaver ponds.

Technical assistance

  • Beavers Northwest is a non-profit based out of the King-Snohomish county area of Washington State. They that specializes in providing technical support to property owners who are experiencing beaver conflicts.
  • Washington State supports live beaver trapping and relocation, which can be used in certain circumstances.
  • The Tulalip Beaver Project relocates beavers to hydrologically impaired tributaries in the upper Snohomish Watershed.

Beaver hunting, trapping, and relocation in Washington

Beavers in the news

A small sampling of beavers in the news relevant to King County beavers.

Who to contact

Services by King County available in unincorporated King County:

Contacts for Washington State including King County: