The following guidelines are based on a limited data set collected to date and, as scientists and environmentalists, our recommendations err on the side of protecting public health based on that limited data. It is also important to note that this study is related only to certain water quality parameters (namely, sewage indicating microbes) and does not detect chemical pollutants or toxins that may be a source of concern in parts of the estuary. Neither Riverkeeper, Lamont-Doherty nor Queens College serve as a public health agency.
In general, Riverkeeper recommends that the average beachgoer, swimmer, boater, and kayaker continue to apply the rule of thumb that has been applied de facto for years: avoid substantial contact with the Hudson River and New York City waterways after heavy rains. The data shows that even days after localized storm events, levels of pathogens can remain above the allowable federal guidelines for swimming. Many stations sampled experienced single day measurements that indicate an increased risk of illness from swimming or direct contact with the river water on that day. Even at sites where conditions were generally acceptable, or that had seasonally acceptable conditions (according to the geometric mean), there was still poor water quality on individual days, particularly after rain events.
People are advised to look on our website for information about the areas they are interested in and to use caution where they note elevated bacteria counts in that area. Riverkeeper does not want to suggest that people stay away from the river or from favorite beaches. This water quality monitoring program is meant to inspire discussion and action towards better pathogen monitoring, and thus, increased protection of public health and the environment.
The Beaches Environmental Assessment and Coastal Health (BEACH) Act of 2000 requires that coastal and Great Lake states report to the United States Environmental Protection Agency (EPA) on beach monitoring and notification data for their coastal recreation waters. The BEACH Act also requires EPA to maintain an electronic monitoring and notification database of that data.
Enterococcus counts are useful as a water quality indicator due to their abundance in human sewage, correlation with many human pathogens and low abundance in sewage free environments.
Federal guidelines for Enterococcus counts are expressed as a Most Probable Number (MPN) per 100 ml of water:
In marine beach areas-
• MPN above 104/100ml indicates a single sample exceedance of the suggested federal guideline for water quality at marine swimming beaches.
• MPN between 35/100ml and 104/100ml indicates a level that if sustained would be an exceedance of the suggested federal guideline for water quality at marine swimming beaches.
• MPN below 35/100ml indicates acceptable water quality.
In freshwater beach areas-
• MPN above 61/100ml indicates a single sample exceedance of the suggested federal guideline for water quality at freshwater swimming beaches.
• MPN between 33/100ml and 61/100ml indicates a level that if sustained would be an exceedance of the suggested federal guideline for water quality at freshwater swimming beaches.
• MPN below 33/100ml indicates acceptable water quality.
Federal guidelines for Enterococcus outlined in the BEACH Act indicate single sample maximum (SSM) values (greater than 104/100 ml at marine beaches and greater than 61/100ml for freshwater beaches) or geometric means from five or more samples (greater than 35/100 ml at marine beaches and greater than 33/100ml at freshwater beaches) be used as water quality limits to close swimming beaches. These values are based on epidemiological studies relating the abundance of Enterococcus to swimming related illness following full body emersion.