A Wet 2018 Saw Sharp Rise in NYC Sewage Alerts: 1 in 3 Days

With climate change driving increased precipitation in the northeast, 2018 brought not only one of the wettest years on record in New York City, but also a sharp increase in sewage overflows. For local waterways, and an antiquated sewer system, it showed.

Diagram courtesy of The City University of New York by Wayworks Designs


With climate change driving increased precipitation in the northeast, 2018 brought not only one of the wettest years on record in New York City, but also a sharp increase in health alerts for sewage overflows. For local waterways, and an antiquated sewer system, it showed.  

Recent data released by the state shows that New York City reported a combined sewer overflow, on average, once every 3 days in 2018. That’s a 44% increase from 2016.

The city’s sewer agency has developed long-term plans, roundly criticized by City Council and community organizations as insufficient, to reduce these overflows over the next two decades. By the city’s own estimates—without accounting fully for climate change—these plans may still leave nearly 20 billion gallons overflowing per year.

Combined sewer overflows and why they cause such a stink in New York City

Almost every time it rains in New York City, raw sewage, pet waste, trash, and polluted runoff flow into waterways where people swim, fish, and boat. In fact, every year more than 20 billion gallons of raw sewage and polluted runoff end up in beloved waterways like the Hudson East, Harlem, and Bronx Rivers, Long Island Sound, Jamaica Bay, Flushing Bay, Newtown Creek and the Gowanus Canal.

While most cities in the U.S. are equipped with separate stormwater and wastewater systems to avoid discharging untreated wastewater into local waterbodies, New York City is among the older U.S. cities, mostly in the Northeast and Midwest, using an antiquated system that collects both stormwater and sewage in the same pipes. This is a problem during heavy rainfall events, when the combined volume of runoff and sewage exceeds the capacity of a wastewater treatment plant or of the sewers themselves. This causes excess untreated wastewater (otherwise known as poop) to flow directly into local waterbodies. It’s called a combined sewer overflow, or CSO.

Unsavory data shows the problem is getting worse

For the past three years, NRDC has been keeping tabs on New York State’s “Sewage Right to Know” data, to see how often New York City issues alerts for combined sewer overflows in local waters. With the year-end 2018 numbers now available, we compared them to prior years, and matched them up against annual rainfall data. The numbers tell a story that is, all at once, both shocking and unsurprising.

From 2016 (a relatively dry year) to 2018, the number of days when NYC reported a combined sewer overflow rose by 44%—from 85 days (as if that weren’t enough!) to 122.

In other words, NYC reported sewage overflows, on average, once every 3 days in 2018. That’s more than twice a week. And it’s up from once every 4 days in 2016. (The rate in 2017, an in-between year for precipitation, was right in the middle, at once every 3.5 days.)


Total CSO Reports

Total CSO Days

Average CSO Days




Every 3 days




Every 3.5 days




Every 4 days

Source: NYC data extracted from NY State Department of Environmental Conservation.

And the trend line for increased precipitation and increased overflows matches almost exactly, as shown below.

NYC CSO reports vs. Central Park precipitation, annual, 2016-2018

Sources: NYSDEC and NOAA

As large as these numbers are, these alerts still understate the problem.

First, they don’t include the billions of gallons of sewage overflows in places like the Hudson River, East River, and Harlem River. Although the state’s “Sewage Right to Know” law requires reporting of all sewage overflows, NYC’s submissions under the law somehow reported ZERO overflows in these places. 

Second, the city says that it does not report every time there's a sewage overflow -- but only when they expect that there's so much overflow that it will exceed the state's weak, outdated limits on bacteria in the receiving waters.  

Third, the city's water quality data, which is collected separately from the Right to Know program, masks the extent of sewage pollution. Unlike the city’s test results, data from community groups' sampling in those same rivers show that 2018 was an especially foul year.

(UPDATE: In May 2019, the city started broadened its  "Sewage Right to Know" reporting, though it still does not cover every overflow. The city's reports now cover more waterbodies, and are based on projected violations of a more stringent bacteria limit in the receiving waters.) 


A new website, Cut the Crap NYC, helps get out the word on NYC’s sewage problems and the solutions, and helps New Yorkers speak out to demand solutions.

This isn’t much a-doo-doo about nothing. Combined sewer overflows contain untreated human waste, trash, ammonia, pesticides, nutrients, petroleum products, pathogenic bacteria and viruses, and other toxins. Those who come into contact with contaminated water as a result of combined sewer overflows can suffer significant health impacts not limited to intestinal illnesses, rashes, and infections.

What can you do?

1.  Make your voice heard.
Send a message to the New York City Mayor, City Council, and the New York State Department of Environmental Conservation and let them know that raw sewage has no place in NYC’s waterways.

2.  Show up.
On April 16th, attend this public meeting for an update on the city’s development of sewage overflow control plans. The city will present options under consideration to reduce overflows to the Hudson River, East River, Harlem River, Long Island Sound, and other major waterbodies. Members of the public will have a chance to ask questions and speak their minds. Here are some suggested questions to ask, courtesy of the SWIM Coalition.

3.  Stay informed.
Sign up to receive alerts from New York State when a combined sewer overflow has occurred in your area. Read up on solutions at Cut the Crap NYC, a new website sponsored by Riverkeeper, NRDC, and Save the Sound. There’s lots more info online at the SWIM Coalition’s website. And follow local experts on social media: @SWIMCoalition (Twitter), @llevine_nrdc (Twitter), @swimmablenyc (Facebook), @cutthecrapnyc (Twitter).

4.  Stay involved.
Get alerts and updates from local groups working to combat NYC water pollution. Sign up for action alerts from Cut the Crap NYC. You can also sign up for e-newsletters from SWIM Coalition. They’ll give you the real scoop on the city’s plans, and let you know about upcoming meetings and events.

5.  Consider your household’s impacts.
Reduce your own flow into the sewers, to help reduce overflows. If you own property, use green infrastructure like rain gardens, rain barrels, green roofs, and permeable pavement to soak up runoff. And if you use indoor running water—as I suspect you do—take advantage of opportunities to conserve, like using water-efficient toilets, showerheads, faucets, and sprinklers