A representation of the Plus Pool in the East River – the actual test pool, scheduled to open in 2025, will be smaller.
Photo by : Pool

Plus Pool, the proposal to put a plus-sign-shaped floating pool in the East River, has long seemed like a fever dream and has tormented us with press releases for a decade. But it looks like the idea that sprang from the designers of Los Angeles-based Playlab and New York architects Dong-Ping Wong and Oana Stanescu is finally moving out of the realm of renderings. Earlier this year, Gov. Kathy Hochul allocated $12 million in funding for the pool, and the city chipped in $4 million (total cost is $50 million), and a smaller test version is currently in the works off Pier 35. This pilot project, which can fit just a few dozen people at a time, is slated to open in 2025. Does all this seem like an extravagant expense for a single pool? Probably. Still, the idea of ​​filtering river water to fill a pool is interesting on a scientific level—and for some, it will fulfill their romantic fantasy of swimming right in the river, like people used to do. But how exactly does this technology work? To better understand the specifics, we turned to Wade McGillis, a mechanical engineer and environmental scientist at the University of Notre Dame who serves as Plus Pool’s scientific advisor.

This interview has been edited and shortened for clarity.

How did you come to Plus Pool?
I was doing water quality measurements in New York and the founders came to me when they started in 2010. I literally partnered with them during the first Kickstarter. I gave them all my monitoring equipment. And their idea of ​​making a big Brita filter for swimming – that’s doable.

Even in something like the East River?
There’s human waste all over our planet. But the amounts are very small – if it’s not raining, you can swim in it. I have citizen scientists who swim in the river all the time. My students have swum in it. Most of the time you can swim in it and of course you shouldn’t open your mouth in certain areas – even in a pristine environment. But there’s a long history of regulation. In some states we can’t reuse rainwater for drinking water, but that’s changing now. So our perception that reused water is gross is slowly being tempered because we have better ways of monitoring it and things like that.

What things need to be filtered out of the East River?
In the region where this takes place at Pier 35, it is mainly sea water. So you really can’t Escherichia coli because E. coli is actually sterilized in seawater. We test for enterococci, another type of bacteria that is also found in human waste. But E. coli and enterococci are fine, they are the pathogens that accompany them – they are just an indication that it is human waste because they are so easy to spot. These pathogens can cause intestinal illnesses ranging from diarrhea to fever.

Where does all this garbage come from?
100 years ago, sewage from waterways and buildings simply flowed into the river. Then sewage treatment plants were built and waste from buildings was sent through pipes that were filtered and sterilized. But New York City’s population has grown so much that these plants are designed to handle a specific flow rate. Have you ever used a Brita filter? A Brita filter is just like our sewage treatment plant – you can only put a certain amount of water through the filter. When it rains, the filter is basically overflowing. When the flow in the pipe gets too high, the water flows into the river. That’s a combined sewer overflow.

So how does the Plus Pool filtering method work?
Well, it evolved throughout the history of Plus Pool. The first incarnation was literally installing a screen. That was unique but difficult to manage. It was a passive filtration system with walls. So you have river water and then you just have these layers around the old pool design. The first was a screen; the next would have been something equivalent to a clay or a synthetic material that sort of filters out the bacteria. It was a great idea, and I personally tested those concepts on the East River just to show that they worked. The problem was that maybe you could have an event – like a heavy rain – that completely contaminated and overwhelmed the system. You had no control. I think that can still work, but our regulation just wasn’t prepared for it.

So it’s a different system now?
I’m not the designer of the current system, but now they’re essentially pushing for active filtration, where, just like in a real pool, you filter the water with a pump. So Plus Pool is like a wastewater treatment plant that takes water from the environment. Plus Pool’s treatment plant pumps water into a big vessel. If the water has something like baby wipes in it — people are under the impression that they’re biodegradable, when in fact they’re basically plastic — the screens remove those big chunks. You just use gravity to separate the big stuff from the small stuff through a screen. Then it gets pumped through a membrane that takes out the small particles. Then if there’s a bunch of bacteria that get through all the hoops, they get eliminated using the same UV light process that gets rid of bad things that get into your drinking water in New York City. The reason for using UV is that you’re not doing anything bad to the water, but with chlorine, you could screw it up and add too much of it.

And if it rained, could you control it?
When it rains, they know to stop pumping so as not to overload the system.

And it would stay clean.
Exactly.

So you basically don’t have to worry about the functionality of the pool’s filter function.
No, not at all. Since they don’t use passive filters now, it’s more robust and weather resistant. And that’s a big deal because sometimes the weather can be tricky.

Could the river overflow into the pool during heavy rain?
No, the whole thing will float. So it will always be able to float. Like Noah’s Ark.

And they are currently testing the entire system.
They’ve started testing and will be doing a full-scale pilot next summer. Also, Pool told me that during this testing, they’ll be sampling six points along this path. So they’re really testing the performance of each individual component. Maybe they need to increase the performance or make a better membrane if it’s not working. It’s good science and engineering to make sure it works.

Can you tell me something about the Lighting system you that you worked on a few years ago – which glowed blue when it was safe to swim and pink when it was not – to continuously detect water conditions?
I had a sensor and I wrote an algorithm that predicted how much rain there was in the watershed and how much pollution there was. And I used real data to link historical rainfall events and the likely pollution in the water. And then I gave that real time to the engineers who built an installation to make lights pink or blue. The reason it was pink or blue was because the Coast Guard only allowed them to use certain colors. You can’t use red and green because that’s for boat navigation.

Is this filter basin system also good for the river?Certainly. It will only do good, except where you get the energy from.