Why Beavers Build Dams

‘Tis the season to clarify an important question when it comes to understanding why, oh why, beavers do what they do! In our education and outreach work with audiences with all ages, this is one of the most common questions we answer- and for good reason! Beavers are well-known for their building behavior which can illicit human reactions spanning from frustration to envy and everything in between.

Beaver Dam in Canaan Valley in West Virginia
Beaver dam in Canaan Valley, WV


A: To impede the flow of water to create a pond. Beavers require water of a certain minimum depth (approximately 3 feet) for a few main reasons:

  1. To dive underwater to escape land predators and obscure the entrances to lodges and dens.
  2. To ensure their pond doesn’t completely freeze during the winter and to maintain an ample food cache.
  3. To travel quickly and safely. Beavers prefer swimming to moving around on land. Especially when hauling larger branches for food or building material!

It can be tricky to tease out the reasons for a beaver’s building from the drastic effects beaver dams can have on wetlands, the surrounding landscapes, and other species. Beavers build and maintain dams year-round (but not always!), but may be especially interested in raising water levels in the fall to prepare for freezing conditions.

Beaver build dams in Clifton Institute
Beaver dam at the Clifton Institute in Warrenton, VA

Dam building beavers rarely build only one dam, although it depends on the specific characteristics of the habitat. Multiple smaller dams in a complex may be built to slow down the flow of water to protect the integrity of the ‘main dam,’ to flood and create canals for travel and foraging, and to access vegetation farther from the original banks. Sometimes they even intentionally open up their own dams to lower water levels.

In short, beavers want to be able to control water depth for their own survival. They often do this by building dams.

Beaver dams come in many shapes and sizes. Beavers building dams in Huntley Meadows in Northern Virginia
Beaver dams come in many shapes and sizes. Here are a series of small dams at Huntley Meadows in Alexandria, VA

Featured image by Ben Goldfarb

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