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Do You Kayak or Wade in the Hudson? Study Reveals Sediment Pollution

The Hudson River is cleaner than it has been in decades, and recreational use of the river is on the rise for everything from kayaking to competitive swim events. Expanded waterfront access in various neighborhoods encourages city dwellers to dip their toes in. And just north of the city, locals routinely swim in the river in places like Westchester’s Croton Point Park.

Water quality is monitored on a regular basis by government agencies and private organizations like Riverkeeper. But a new study suggests that testing surface water from the middle of the river might not provide a complete picture of health risks.

The study published in Science of the Total Environment found that sediment at the Hudson shoreline is often loaded with fecal indicator bacteria (FIB). The study also found these bacteria in the sediment are easily stirred up by stepping into the waterfront muck or sand. Once disturbed, the bacteria get distributed in the shallow water near the shore.

Professor Gregory O'Mullan on a boat in the waters around Manhattan
Gregory D. O’Mullan

The study was led by Gregory D. O’Mullan, professor at Queens College and The Graduate Center, CUNY, and Andrew R. Juhl of Columbia University’s Lamont-Doherty Earth Observatory.

The researchers measured two common fecal indicator bacteria, enterococci and Escherichia coli (E. coli). It found that “shoreline water samples had higher average FIB concentrations than samples collected nearby but further from shore.” Enterococci in shallow water at each location also exceeded federal Environmental Protection Agency guidelines for recreational waters.

Usually, elevated levels of FIB in waterways are temporary, related to the discharge or overflow of untreated sewage. Those incidents often correlate with heavy rains in warm weather. But soil, sediment and sand can “act as naturalized secondary habitat for FIB,” allowing the bacteria to thrive, unrelated to any sewage discharge events.

Samples for the study were collected at 11 points on the river from Queens to the Hudson Valley. The sites with the least contamination were found to be the most northerly sites.

“Understanding and predicting FIB in estuarine waterways may require including sediments as an indirect FIB source in addition to direct sewage and other inputs,” the authors wrote. “The observed patterns of sediment in FIB are relevant for sewage control, monitoring, and recreational use management of the Hudson River Estuary, as well as other urban estuaries.”