As beaver dams turn Maple Valley land into a swamp, Curley explains why beavers do what they do

Several Maple Valley homeowners along Taylor Creek have claimed that beaver-built dams have turned dry land into a swamp, but state wildlife officials stated they can’t force a resolution without a neighboring landowner’s permission.

“That used to be all dry land,” Michael Upton, a Maple Valley homeowner, told KIRO 7. “Now it’s all taken over by water. It’s not just water, it’s swamp water.”

Upton also said the land is at its lowest point right now because of the lack of rainfall. But when rain comes, several homeowners fear flooding could wipe out some of the homes in the area.

Under Washington law, removing beaver dams is permitted if a dam threatens private land, but the Washington Department of Fish and Wildlife (WDFW) said they cannot require a landowner to remove beavers on their property if they do not want to.

WDFW can issue permits to authorize beaver relocation under certain conditions, but the department believes removing dams rarely solves the problem, as beavers often quickly return to rebuild.

Why do beavers build dams anyway?

With beavers causing havoc locally, KIRO Host John Curley asked traffic reporter Nate Connors, “Why do beavers build dams?”

“Well, because that’s their house,” Connors said. “And it makes a pool of water to make it easier for them to go fishing.”

Connors’ answer reflects the common assumption that beaver dams primarily function as flood control for their lodges, or to create ponds for foraging. Curley then asked a follow-up, citing a decades-old scientific study with a different explanation.

“Joe, why do beavers build dams, according to a 1960s experiment in Sweden?” Curley asked his producer Joe Wallace.

“Because they hate the sound of running water,” Wallace answered.

“That’s right!” Curley said.

The study Curley referenced was conducted by Swedish zoologist Lars Wilsson in the 1960s. Wilsson raised beaver kits in isolation, without exposure to adult beavers or a natural river, to determine whether dam-building was learned behavior or instinct. When he played a recording of running water through a hidden speaker, the young beavers immediately worked to bury it in sticks and mud, treating the sound itself as the leak. In a follow-up test, Wilsson ran water silently through a clear pipe while playing the recorded sound elsewhere; the beavers ignored the visible water entirely and buried the speaker instead, suggesting the sound of moving water, not the water itself, triggers the building instinct.

Curley said the finding reframes what a beaver dam is actually for.

“Now you know the rest of the story,” Curley said. “It’s not about building a house.”

“Never heard that in my life,” Connors said. “It’s beaver country.”

Watch the full discussion in the video above.

Contributing: KIRO 7

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