What Frick Park’s beaver means for the health of the restored Nine Mile Run

Castor is the second beaver to be spotted in the park in recent years, according to Heide. The first one appeared in Nine Mile Run in 2019, likely having migrated up from the Monongahela River, the waterway that sits at the mouth of the stream.

Heide said that the beaver stayed in the area for about a year, but no mates or kits (the term for baby beavers) were spotted with him.

“He moved on, we assume, for mating season,” Heide said.

So far, Castor has appeared alone at Nine Mile Run, too. Heide said while beavers are friendly within their family units, they’re territorial creatures, with just one family inhabiting a single section of a waterway at a time.

In any number, though, Heide said the presence of beavers is a sign of a healthy ecosystem where sewage and industrial waste once dominated.

“They are known as nature’s engineers,” she said enthusiastically. “They’re the only one of the only species that can change their environment and alter the hydrology.”

Creating a healthier Nine Mile Run

Nine Mile Run underwent a $7.7 million restoration from 2003 to 2006. At the time, it was one of the largest urban-stream restoration projects in the United States.

Prior to the project, the stream had been known to locals as “Stink Creek.” Toxins leached into the creek from a slag heap — a 120-foot high pile of industrial waste — covering 238 acres along the stream. Sewer lines discharged into the water, and much of the waterway had been diverted from its natural path.

This years-long effort to detoxify the stream, led by the City of Pittsburgh and the U.S. Army Corps of Engineers, included rerouting the stream channel by adding curves and ripple rocks to slow down the water and the rate of flooding.

A decade and a half later, fish and beavers have continued the work of improving the surrounding wetland environment.

For instance, beavers’ chomping habits can be useful in shaping a climate-resilient landscape.

“See how clustered and how tight they are,” Heide said pointing to a group of streamside willow branches. “That’s actually really bad. They’re even starting to uproot themselves because of how heavy they are.”

But beavers love to eat willows, which grow back once cut down.

“It will cut those down and then they can regenerate into like a healthier cluster,” she explained.

Doing so helps protect the stream bank from erosion. Heide said the parks plan to plant more willows this spring and will hold several willow staking events where residents can get involved.

To protect the trees they want Castor to stay away from, park rangers and conservation groups put protective cages around nearby trunks, prioritizing those that are young and native to the northeast, like oaks, aspens and maples.

Invasive species taking over the park’s wetlands, like Tree of Heaven and Japanese honeysuckle, on the other hand, are fair game for Castor to munch on, helping park staff out through a more organic form of invasive plant management.

Maintaining a floodplain where wildlife can thrive

Heide said it’s unlikely beavers will ever build a successful dam on Nine Mile Run. During storm surges, the area is susceptible to intense flooding that dams would likely not withstand.

Still, if Castor or any other beaver in the park was able to complete a dam, Heide said it would be another step toward successful environmental restoration. For one thing, it can cause flooding that brings up nutrients and seeds from the water into the soil, sparking a surge in vegetation for wildlife to eat.

To protect native trees from beaver teeth, park rangers and conservation groups put protective cages around saplings in the surrounding wetlands. Photo: Jillian Forstadt / 90.5 WESA News

At the same time, dams can further reduce the rate of flooding by slowing down floodwaters while filtering out pollutants that travel downstream.

Still, conservationists in Pittsburgh want to prevent any sewage or pollutants from getting to the beavers in the first place so that they, as well as all the other species that have come to inhabit this section of the park, have a place to thrive.

Upstream Pittsburgh, formerly the Nine Mile Run Watershed Association, is one of the groups leading that charge. Executive director Mike Hiller says despite being a healthier waterway, the urban stream still faces excessive stormwater runoff and sewage overflows, as well as bank erosion and pollution.

Prior to the restoration, stormwater overflows had caused the stream to straighten out, making it what Hiller called a “perfect vessel” to carry fast-running, and often polluted, stormwater into the Monongahela River.

While the restoration reshaped the landscape into one full of water-slowing curves and meanders, overflows remain one of the greatest threats to sustaining a robust ecosystem at Nine Mile Run.

“That’s why a lot of our work is focused in the upper watershed to capture the rainwater where it falls and hopefully, project by project, we’re reducing that overflow, a little bit at a time,” Hiller said.

The nonprofit has partnered with municipalities throughout the watershed to address the causes of excessive runoff. That includes implementing stormwater management systems and installing green stormwater infrastructure to reduce runoff, such as tree pits and rain gardens.

“The issues are coming from too much stormwater hitting hard surfaces in the upper watershed, running off into stormwater catch basins and then just being spewed into the stream when it rains,” Hiller explained.

Much of their work focuses on diverting that water from hard surfaces that cause runoff and reduce the overall volume entering the storm sewer system. In Homewood, the nonprofit built a rain garden that captures runoff from the roof of the Pittsburgh Housing Authority’s North Family Reinvestment Center and pipes it underneath hard surfaces to the infiltration area.

Hiller said the organization hopes to continue that work to protect the health of habitats throughout the watershed and restore other parts of the park, like the Fern Hollow Valley.

The presence of a beaver, he added, is a sign that they are headed in the right direction.

For those who want to see the beaver, Heide advises people not to get their hopes up.

“He’ll probably become more and more elusive as we get into the colder and colder weather,” she said. “Just like us, we don’t want to be out in the cold. Neither does he.”

In the event he is spotted, Heide stresses that people give him space, and keep any dogs in the park on leash.

“That will ensure that this beaver is safe for future years to hopefully come back.”