A bold step toward swimmable waters in New York City’s East River concluded this November with the completion of a 90-day test of the +POOL filtration system. The results, released by the +POOL team, demonstrated substantial progress in making this project (conceived of in 2010) a reality while uncovering new challenges along the way.

The +POOL team conducted more than 3,015 discrete tests during their fieldwork, focusing on both physical and chemical parameters like pH, turbidity, and temperature, as well as microbiological indicators such as Enterococci and E. coli. The filtration system achieved a major milestone: reducing bacteria levels to below detectable limits in the lab, meeting the water quality standards necessary for safe swimming.

One significant element was missing from the test — New York City’s typically unpredictable weather.

“We weren’t able to test the system against major storms or rain events, simply because they didn’t occur during the testing period,” the team stated in a press release.

On the upside, record-breaking warm temperatures in October highlighted the potential for an extended swim season, offering a glimpse into how climate change might shape urban swimming in the future.

A collaboration with environmental consulting firm Roux brought an unexpected discovery: the East River abounds with underwater life. Using an underwater drone, the team cataloged an array of marine life at the proposed site, including blue crabs, black sea bass, red beard sponges, and vibrant algae. This research forms part of a comprehensive sanitary survey designed to meet newly established New York State Department of Health guidelines for new bathing facilities.

The team also faced an unexpected challenge: seaweed. The prefilter collected much more seaweed than anticipated, requiring manual cleaning, and significant algae growth occurred in the test pool. The team allowed the algae to flourish as part of an experiment to determine cleaning schedules for the full-scale pool launching next summer.

This seaweed abundance sparked creative discussions about its potential reuse, with the +POOL team remarking, “East River seaweed ice cream, anyone? (Maybe not quite yet!)” The testing phase also addressed how often the filters will require backwashing to maintain optimal function. Fouling of the membranes occurred more slowly than expected, reducing the need for frequent maintenance.

While the +POOL water will remain chemical-free, periodic deep cleaning of the filters is planned, with protocols refined through this testing period.

With their prototype field tests wrapped up, the +POOL team is now racing toward their next milestone. Construction is underway on a custom barge that will host the fullscale +POOL, and plans are in motion to train facility operators for a final round of testing in summer 2025.

“This has been an incredible collaboration of innovators and engineers,” the team stated in their release. “We’re staying on an aggressive timeline to bring safe river swimming to New Yorkers as soon as possible.”

Stay tuned for more updates on +POOL as it moves toward completion.