Newly flowing Manayunk Canal will soon be home to thousands of mussels — but not for eating

Lance Butler, a senior scientist with the Philadelphia Water Department (PWD), and his team cultivate up to 50,000 freshwater mussels annually in the Schuylkill, deploying them as tiny but powerful natural water filters. It’s both low-tech and cost-effective.

Now Butler is taking his experiment upstream to an unlikely place: the Manayunk Canal.

The waterway was a mere trickle until its recent reconnection to the Schuylkill at Flat Rock Dam. PWD invested $20 million to reconstruct the dam, restoring the canal’s free-flowing waters after decades.

His project aims to understand how mussels respond to water quality in urban settings, as each mussel can filter five to 10 gallons of water daily and live for 80 years or more. The work is part of a larger effort to use nature-based solutions for improving urban waterways.

To track their progress, the mussels will be outfitted with radio transmitters, enabling Butler to monitor their growth and ecological impact.

“We have 2,000 to 3,000 now in cage systems,” Butler said. “The next phase would be to plant them in the sediment of the Manayunk Canal. Then the next phase would be to radio tag those mussels, or a subset of them, and then actually let them go. We’ll go up and down in a boat and detect where they are, how they’re living, and what’s their growth rate.”

Mussels are bivalve mollusks that live on the bottom of waterways.

Once, the rivers and streams of the Delaware River watershed, which includes the Schuylkill, were thick with beds of freshwater mussels, which are not edible — unlike the saltwater species that inhabit the Jersey Shore.

But dams, water pollution, and stressors besetting waterways caused them to all but disappear.

Freshwater mussels are considered the most imperiled of all plants and animals, with 75% of 300 North American species in trouble.

In an attempt to bring freshwater mussels back to Philly, PWD created a mussel hatchery in the Schuylkill in 2017 in partnership with the Academy of Natural Sciences of Drexel University, the Partnership for the Delaware Estuary, and the Fairmount Water Works.

Butler and program specialist Shannon Boyle lead the daily efforts to get freshwater mussels to propagate to improve river water quality. They work out of the 600-square-foot hatchery at Fairmount Water Works but plan to relocate to a new facility at Bartram’s Garden, also on the Schuylkill. There, they expect to produce up to half a million mussels per year.

In a process known as biofiltration, they draw water through siphons and filter out particles as the water passes through their gills. The action removes suspended particles, algae, bacteria, and other microscopic organisms from the water, improving its clarity.

Mussels can filter pharmaceuticals, personal care products, herbicides, flame retardants, E. coli, and avian influenza, according to the U.S. Fish and Wildlife Service. However, that same pollution can also harm the mussels.

Collectively, mussels can process significant volumes of water, making them valuable tools for natural water purification and ecosystem restoration.

However, Butler said, invasive species of mussels are also a concern.

“Zebra mussels are particularly concerning because they can attach to almost any surface and multiply rapidly, causing damage to infrastructure and disrupting ecosystems,” Butler said.

Butler said PWD’s Flat Rock Dam project was a catalyst for attempting to propagate mussels in the Manayunk Canal.

The dam is on the Schuylkill where Philadelphia and Montgomery Counties meet. It was built in the 1880s to support the coal industry by funneling water to factories that once lined the canal. The canal was closed in the 1940s, which diminished fresh water from flowing in from the river and resulted in stagnant, smelly water, along with accumulated trash, in the canal.

PWD spent decades planning reconstruction of the Flat Rock Dam Betterment Project and started construction in 2022. The gates opened April 14, releasing more water as the weeks went by. The dam will be fully open later this month, bringing the water in the canal from a rate of one cubic foot per second before the project to about 100 cubic feet per second.

That new flow of fresh water was welcomed not only by Manayunk residents, but also by Butler, who saw it as an opportunity to continue his work with the mussels.

“This is an advancement,” said Butler, who is pursuing a Ph.D. “When we first started, I was sort of on the fence. I thought, ‘I don’t know if we can do this. Is it really feasible?’”

He had some setbacks. Hurricane Ida in 2021 flooded the Schuylkill and destroyed the mussel laboratory. Butler had to fish his equipment out of the Delaware River. And COVID-19 stopped progress for a year.

But the success of the program led him to believe it would work in Manayunk, too.

He now has multiple facilities to grow the mussels, including Green Lane Reservoir in Montgomery County and the Discover Center on Strawberry Mansion Reservoir in Fairmount Park in Philadelphia.

To cultivate the mussels, Butler and his team use a natural process that depends on a parasitic relationship between the mussels and fish.

They take larvae of female mussels and place them on the gills of fish in a 150-gallon holding tank. Typically, Butler uses a species of mussel called an alewife floater.

His lab uses largemouth bass, brook trout, perch, or other fish, depending on the species of mussel. A single fish can carry up to 500 larvae on each gill.

“We’re continuing to refine our techniques and doing very well,” he said. “We are seeing that they filter on average around six to six and a half to seven gallons per day. Bring that up from 2,000 mussels to 100,000 to a million. Think about how many gallons per day the could process. At that point, they’re just basically a treatment plant.”