The Fairmount Water Works is showing off its mussels.

A new, permanent exhibit at the former municipal pumping station near the Art Museum of Philadelphia, opening Friday, will feature mussels as nature's water-filtration system.

The exhibition doubles as an experimental science station.

Mussels — the black bivalves that are so delectable in a white wine broth — are able to filter 20 gallons of water a day. That's 20 gallons per mussel; a bank of thousands of mussels could keep a whole river clean.

Unfortunately, for about 200 years, we have treated our rivers as industrial sites, and mussels living on a diet of toxins have died off.

The creatures also rely on passing fish to reproduce, through a complex symbiotic process of fertilization, but river dams block the traffic of fish, making mussel reproduction all but impossible. Waterways once teeming with colonies of mussels had been reduced to nearly nothing.

But now, mussels are poised for the comeback.

"We've taken down dams, water quality has much improved," said Angela Padeletti, a senior science coordinator with the Partnership for the Delaware Estuary. "For those reasons, we think we can introduce these babies back into the river system, and they will survive and thrive."

Padeletti is talking about freshwater mussels, which are not suitable for eating so there is little commercial incentive to grow them. However, they are ecologically valuable as water filters. And a single mussel can live for a century, constantly filtering for its food.

The Pew Center for Arts and Heritage has given $300,000 to the Fairmount Water Works, along with the Academy of Natural Science of Drexel University and the Partnership for the Delaware Estuary, to develop a viable mussel hatchery as well as an exhibition surrounding it.

These mussels never relax

The purpose is twofold — first, to teach people how important mussels are to our waterways.

The problem is mussels might be the least sexy of all aquatic life. They are literally bottom feeders.

"A mussel looks like a rock. A mussel doesn't have eyes," said exhibition designer Victoria Prizzia of Habitheque, Inc. "How do we play with the characteristics of the mussel, but do it in a way that doesn't diminish the authenticity of the story. We didn't want to turn this into a cartoon."

She did eventually turn it into a cartoon — an animation panel in the exhibition space showing a mussel with big google eyes. But she did not give the mussel a name or a voice; it's not "Finding Nemo." It quietly, resiliently, goes about filtering water.

"All of our characters — all 27 river characters we share in relation to the mussel — carry a message of diversity. Mussels are a big part of that, as ecosystem engineers," said Prizzia. "Meaning, they create healthy habitat for other species. It's not just fending for themselves, they are fending for other aspects of the river. They are part of a team."

The second purpose of the mussel hatchery is doing the hard science of developing a mussel population. The lab has 20 tanks, in which fish are carefully introduced to floating baby mussels, which naturally attach themselves to the passing fish. Eventually the baby mussels release themselves from the fish to grow on their own.

Those adolescent mussels are gathered into baskets, and sunk into area ponds with enough floating nutrition to keep a growing mussel fed. The Partnership for the Delaware Estuary has created relationships with Longwood Gardens, Winterthur House and Garden, and the East Park Reservoir in Philadelphia to help nurture the hungry mussels.

When the mussels mature to about the size of a thumbnail, they will be released into selected areas to grow into adults. The Tacony-Frankford Waterway in Philadelphia has already been the site of mussel habitation experiments.

Water department keeping tabs

The Philadelphia Water Department, watching closely to see where the mussels are able to repopulate the riverbanks, will consider how to use them as part of the municipal water-processing system.

"We have an agreement [Philadelphia Water Department, Academy of Natural Science, and the Partnership for the Delaware Estuary] that we are working to find a location near the city of Philadelphia where we can raise mussels to a level where they can do that hard work for cleaning our river waters," said Karen Young, director of the Fairmount Water Works.

"Right now we're looking at the demonstration of that process. The application of that is going to come later," she said.