Ossining Waterfront

Citizen Testing Sites

Water Quality Conditions by Location

Recent Samples Historical Statistics
Site Name (Watershed) Sample Date [i] Entero Count

Entero Count

Enterococcus (“Entero”) is a fecal indicating bacterium that lives in the intestines of humans and other warm-blooded animals.

[i] 4 Days Total Rain (in)

4 Days Total Rain (in)

The combined rainfall for the day of sampling, prior day, two days prior and three days prior. More than 1/4 inch is considered a “wet weather sample.”

[i] Number of Samples

Number of Samples

Total number of samples included in these calculations.

[i] Geometric

Geometric Mean

A measure of central tendency (a weighted average) used by NYS DEC and the US EPA to assess water quality. The geometric mean is defined as the nth root (where n is the number of samples) of the product of the Enterococcus measurements. A geometric mean over 30 fails the EPA criteria for safe primary contact.

[i] Maximum


The highest Enterococcus count we have recorded at this site (“>” indicates an unknown number greater than this number and reflects the upper limit of our scoring ability for this sample).

[i] Minimum


The lowest Enterococcus count we have recorded at this site (“<” indicates an unknown number less than this number and reflects the lower limit of our scoring ability for this sample).

Individual Entero Counts by Site

Note: multiple counts of the same value will overlap and appear as one dot.

Water Quality*

Acceptable (0–60) Beach Advisory (61+)

*Single sample thresholds;
Enterococcus count per 100mL

Prior Four Day Rainfall
(in inches)

Dry Weather (0–0.25) Wet Weather (0.25+)

Geometric Mean*

Acceptable (0–30) Unacceptable (31+)

*Weighted average of multiple
samples; Enterococcus count
per 100mL

Enterococcus is an EPA-approved fecal contamination indicator.

Ossining waterfront samples are taken by Ossining High School students and processed at OHS, using methods and study designs that are consistent with Riverkeeper’s Hudson River and Community Water Quality Testing programs.

Until the mid-1900’s, the Ossining waterfront was home to a Hudson River swimming beach, until the floating dock was deliberately sunk. Riverkeeper has sampled the Ossining waterfront, near the former beach site, during water quality patrols since late 2006. Our results show that the site nearly meets the EPA’s recommended criteria for long-term beach management.



The Ossining waterfront is sampled by Ossining High School students. Students process the samples at Ossining High School. In 2015, OHS students are testing the water weekly. This will help us learn more about the sources of contamination at the former beach, and start a conversation about what it would take to re-open this swimming area.

Read more about this sampling project on the Riverkeeper Boat Blog.

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