Water quality in the Harlem River in New York has improved greatly since passage of the Clean Water Act in 1972, though there are still instances where it doesn’t meet state and federal standards according to first time analysis of the river data by the U.S. Geological Survey.

Specifically, although concentrations of dissolved oxygen and fecal indicator bacteria have improved, they do not consistently meet standards for good ecological health. Other important environmental indicators have also improved the past 20 years, such as concentrations of ammonia and suspended solids, which are good indicators of how well wastewater treatment plants are working.

Even with the improved water quality, the Harlem River still retains its “Class I,” or impaired, designation under New York Department of Environmental Conservation regulations, which means communities surrounding the river cannot fully utilize this natural resource. Boating and fishing are permitted in the Harlem River, but swimming is not recommended, and certain shellfish caught in the river should not be eaten.

“The actions that have been taken the past 40 years have resulted in significant improvement to the river’s water quality,” said Shawn Fisher, a USGS hydrologist and author of the study. “Even with the changes, though, the river remains on the impaired waterways list and while boating and fishing are permitted, swimming is not recommended. It is also advised that certain shellfish and finfish caught in the Harlem River should not be consumed. It’s likely to remain on the impaired list until the potential for sewage discharge into the river through combined sewer outflows has been eliminated, and the riverbed sediment is remediated.”

Fisher added that a comprehensive assessment would be needed to measure concentrations of metals, PCBs, and other regulated and legacy pollutants, to identify which contaminants remain in the river; determine how they can be safely removed; and figure out how to prevent them from entering the river in the future.

The Harlem River in New York City has provided the city’s communities with recreational opportunities like boating and fishing since the 1700s. Over time, human activities along the Harlem River, such as shipping, industry, and waste disposal, have severely affected the overall water quality of the river.

“The New York City Department of Environmental Protection has a great water-quality dataset dating back over 100 years,” said Fisher. “This historical information, combined with water quality data still being collected today, is invaluable to better understand the dynamic changes that occur on a daily basis.”

The USGS publication Historical water-quality data from the Harlem River, New York, SIR 2016-5044, was developed in cooperation with the New York City Department of Environmental Protection Bureau of Wastewater Treatment.

Image: Photograph of the Harlem River and Washington Bridge circa 1905, looking northward. The bulkhead in place along the west riverbank (in New York County) supports the adjacent Harlem River Speedway. The east riverbank (in Bronx County) is relatively undeveloped and the shape of the bank is unaltered. Source: Library of Congress.