Lake Sammamish beaver invasion: Parks and City struggle to balance nature and community needs

One of the benefits of living near the foothills of the Cascade Mountains is the way daily life brushes up against nature. And it's just this proximity that is creating a beaver conflict at Lake Sammamish State Park.

Sink hole caused by Lake Sammamish beaver colony.

One of the benefits of living near the foothills of the Cascade Mountains is the way daily life brushes up against nature. It’s not uncommon for residents of Issaquah and Sammamish to encounter a deer peeking out from the brush alongside the road during their morning commute, or to watch a bald eagle circling above a nearby field in search of its afternoon meal.

And it’s this proximity of man with nature that is creating a conflict at Lake Sammamish State Park.

In 2007, the City of Issaquah completed a restoration project on the ditch known as Pickering Creek, which drains stormwater from downtown Issaquah into Tibbetts Creek, and eventually into Lake Sammamish. This project, along with programs undertaken by the park, widened the stream, removed accumulated sediment, cleared away invasive plants, and reintroduced native vegetation. The goal was to reduce the risk of flooding during periods of heavy rain, and during the spring runoff.

The project improvements also enhanced the ecosystem around the streams, and it didn’t take long for nature’s own engineers to see these changes as an opportunity to acquire lakefront property.

“We currently have two active [Beaver] dams, but we’ve had as many as seven,” said Washington State Parks Northwest Region Steward Steven Starlund.

Dams are the most recognizable feature of Beaver habitat. Constructed of twigs, branches, mud and other debris, the dams block rivers and create ponds where the Beavers can then build their lodges. Both of these structures serve as protection, from predators and from the elements, as well as becoming places to store food.

Like any prospective homeowner touring the local real estate market, Beavers look for property that provides the essentials – slow moving water and an abundance of natural resources. The relatively flat ditches and streams of the Issaquah floodplain are an ideal base for this kind of construction, and the newly planted vegetation provides both building materials and food.

When Beavers move in, the resulting dams and ponds can be an ecological boon for the surrounding area, creating biodiversity, reducing erosion and purifying the water of toxins.

But they can also present real hazards for humans and other animals. During heavy rains, water behind the dam can back up and cause flooding. When a dam breaks, it can cause flash floods downstream.

“For us, they’re drowning out our restoration efforts,” explained City of Issaquah Surface Water Manager Kerry Ritland. “Beavers like to deforest our restoration efforts. During a big rain, this could create flooding issues in downtown.”

At the park the problem goes beyond potential flooding and drainage concerns. The Beavers have chosen to burrow under the road that leads into the park instead of building separate lodges. This is creating sinkholes and a potential public safety hazard.

Solving the problem of the park’s newest residents is no easy task.

“It’s a complicated process,” said Starlund. “Up until now, we’ve tried to live with the Beavers, but they keep thwarting our efforts.”

During salmon spawning season, or if there’s a threat of flooding, the park service has breached the dams in an effort to manage the problem.

“Within 24 hours, the Beavers have rebuilt it,” he said. “They’re very clever, industrious.”

This summer Washington State Parks, along with the City of Issaquah and the Muckleshoot Indian Tribe, are putting together an adaptive management plan they will present to the Department of Fish and Wildlife. The most humane solution at this point seems to be to relocate the beavers to another area. But not every property owner is willing to welcome the rodents with open arms, so the group may be forced to consider lethal control.

Starlund summed up the dilemma these groups are facing.

“We have to be sensitive to both wildlife and people,” he said. “It’s not easy to have wildlife in an urban area.”


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