A river runs through it: swimming returns to the riverbanks thanks to eco-friendly pool designs.(ENVIRONMENTAL POOLS)(hudson river)

Swimming in the Hudson River used to be followed by a trip to the hospital for a tetanus shot. Alan Zollner and his club think it's time for swimmers to take the river back.

"The river is getting cleaner," said the president of the River Pool at Beacon, a nonprofit project headed by the Beacon Sloop Club in Beacon, N.Y., 60 miles north of New York.

The project--a $100,000 floating circle of interconnected modular fiberglass and a webbed nylon bottom--allows water, light and fish to flow through the pool. A smaller prototype will be installed by June.

Though the water in many rivers is getting cleaner thanks to provisions such as the Clean Water Act, the bottom sediment is still quite toxic. Also, environmental groups worry about upsetting delicate ecosystems. Floating river pools solve both problems with a design that keeps swimmers away from that area and safe from sweeping currents.

The idea of floating pools conjures turn-of-the-century images of wood bathhouses and river docks filled with swimmers. These historic flow-through bathhouses are where architect Meta Brunzema first got the idea.

In fact, environmentalists were the ones who opposed the idea, recalled the owner of New York-based Meta Brunzema Architects, because such a structure would create shading and interfere with the river's ecosystem. With that in mind, she set to work designing a transparent pool, now being adopted by the River Pool at Beacon. She said there's huge interest for her design along the Hudson River.

Because fish can swim through, Brunzema expects the pool to be more than a place to swim. It will be an environmental classroom, too.