Water Quality In NYC

How Clean Is the Water?

The City has come a long way to improve the quality of our rivers, creeks, the harbor and the ocean in the last several decades since the passing of the federal Clean Water Act. Many of our waterways are now swimmable. Except when it rains.

Much of the City is served by what is called a combined sewer system in which one set of pipes carry both household waste water and runoff from the streets. On a dry day the system works fine but on rainy days the increased volume of water (a mixture of waste water and stormwater) overwhelms the treatment plants and this mixture is often discharged into our waterways without any treatment. This is called Combined Sewer Overflows, or CSOs. About two thirds of the City is served by the combined system, making this a serious problem that prevents us from meeting the federal Clean Water Act goal of fishable and swimmable waters.  

NYC Department of Environmental Protection (DEP) has been testing water quality since 1909 and has made its entire dataset available online. Since 1986, DEP has tested for Fecal Coliform, a sewage-indicating bacteria. Fecal Coliform is found in human and animal feces, and is not necessarily harmful itself but indicates the presence of sewage and potentially disease-causing bacteria (pathogens) in the water. The interactive map below shows Fecal Coliform results since 1986. According to New York State standards, the number of Fecal Coliform colonies in a 100 milliliter sample should not exceed 1,000 colonies (shown in red) and the 30-day average* should not exceed 200 colonies (shown in yellow). Samples with less than 200 colonies indicate good water quality (shown in green). The temporal map shows that while water quality has dramatically improved over the decades, there are many tributaries that continue to show consistent failure to meet water quality standards.