Why Do Beavers Build Dams?

Beavers and their dams play an important role in nature. Because of the dramatic effects their dams have on surrounding ecosystems, these mammals are considered a keystone species. By constructing dams they create wetlands -- lush environments which attract fish, ducks, frogs and other creatures. However, beavers can become a big headache for farmers and landowners -- a problem we'll examine later in this article.


Beaver Dams: The Good and the Bad

With their large front teeth, a pair of beavers can easily chew through the trunk of a medium-sized tree.
Alan and Sandy Carey/Photodisc/Getty Images

Aside from making cozy homes for their families and their friends, beavers play a leading role in nature's big picture when they build dams. More than most other environments, wetlands depend heavily on beaver dams. Although in the United States they've suffered from urban development and pollution, wetlands host a variety of animal species. One nonprofit organization devoted to beavers claims that almost half of endangered and threatened species in North America rely upon wetlands [source: BWW]. Wetlands also absorb large amounts of water, which counteracts the effects of heavy rainfall and can prevent potential floods. In addition, beaver dams act as natural filters that keep sediment and toxins from flowing into streams and on into oceans.

Although beavers play an important role in the ecosystem, they can also cause problems that are sometimes more than a nuisance. Beaver dams can actually cause flooding. This can wipe out land that farmers need for crops or livestock. Experts estimated that the U.S. timber industry suffered more than $22 million in damage in a single year due to flooding caused by these dams [source: Vantassel, et al]. It doesn't stop there. This flooding can endanger public safety by saturating the soil and making roads, bridges, train trestles and levees unstable. Also, beavers, with their sharp teeth, can chew through valuable, rare or important trees, and felled trees can pose a hazard to utility lines and buildings.


Government agencies, environmental organizations and others work with landowners and farmers to come up with environmentally-responsible methods of beaver dam control. Sometimes it's by humanely trapping and removing the beavers, although more beavers often move in. In other cases, landowners use beaver pipes -- corrugated plastic pipes stuck in a beaver dam and routed to a specific location -- to control and prevent flooding caused by dams. Yet others build pre-dams -- fences that encourage beavers to build in a desired location [source: Brown, et al].

Another tactic is to install specially-designed fences in waterways to keep beavers from building there in the first place. Low-voltage electric fences are also used to keep beavers off of land -- a concept similar to fencing cow pastures.

What's more, some people paint trees with a special repellant that keeps beavers away. Homeowners can wrap the lower portion of smaller trees and ornamental shrubs with wire, but it's not effective for keeping beavers from chewing on large trees. In some situations, government agencies compensate those who guard beavers and their wetland habitats.

Depending on whom you ask, the busy beaver and his powerful dam can be a blessing or a curse. For more information about beavers, beaver dams and other related topics, follow the links on the next page.



Beaver Dam FAQ

Why do beavers build dams?
Beavers build dams for protection from predators. Contrary to what many people think, they don’t live underwater, but rather the dam acts as a protective lodge for them. These dams block water from flowing out of the pond, creating deep water that makes them feel safe.
Are beaver dams good?
Beaver dams create wetlands - lush ecosystems that support a large variety of animal and plant life. These wetlands also neutralize the impact of heavy rainfall and prevent flooding. Additionally, beaver dams prevent toxins and sediment from filtering into streams.
Why are beaver dams bad?
Beaver dams can cause flooding, as well as damage lands that farmers use for livestock or crops.
Is it illegal to tear down a beaver dam?
According to state laws, disturbing a beaver’s activities or removing a beaver dam is a misdemeanor. You need a license or permit to tear down a beaver dam.

Lots More Information

Related HowStuffWorks Articles
More Great Links

  • "Beaver Biology." Beaver Solutions. http://www.beaversolutions.com/about_beaver_biology.asp
  • "Eager beavers give estate a dam." BBC News. June 15, 2008. http://news.bbc.co.uk/2/hi/uk_news/england/devon/7455673.stm
  • "How Beaver Problems Develop." King County. April 11, 2008. http://www.kingcounty.gov/environment/animalsAndPlants/beavers/problems-develop.aspx
  • "Solving Problems with Beavers." The Humane Society of the United States. http://www.hsus.org/wildlife/urban_wildlife_our_wild_neighbors/solving_problems_with_your_wild_neighbors/solving_problems_with_beavers.html
  • "The Beaver." Beavers: Wetlands & Wildlife. http://www.beaversww.org/beaver.html
  • Fall, Samuel. "Beaver Pictures & Facts." 2007. http://fohn.net/beaver-pictures-facts/
  • Grannes, Steven G. "Beaver Dam Information." Jan. 14, 2008. http://www.beaverdam.info/
  • Vantassel, Stephen, et al. NebGuide. Controlling Beaver Damage. University of Nebraska-Lincoln Extension, Institute of Agricultural and Natural Resources. http://www.ianrpubs.unl.edu/epublic/pages/publicationD.jsp?publicationId=47
  • Wachtel, Beverly. "Beaver Dam." Earth & Sky Teachers Center. http://www.earthsky.org/teachers/article/beaver-dam
  • Waubaugh National Wildlife Refuge and Wetland Management District. U.S. Fish & Wildlife Service. http://www.fws.gov/waubay/terms_definitions.htm