Saw Mill River

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.

Samples taken by citizen scientists and processed at Sarah Lawrence College Center for the Urban River at Beczak, using methods and study designs that are consistent with Riverkeeper’s Hudson River and Community Science programs.

Read Riverkeeper’s 2021 data report for the Saw Mill River Watershed.



The Saw Mill River drains a long, narrow basin in Westchester County. The river’s course passes through residential, commercial, urban and forested areas. Both the river and its watershed have been extensively modified by urban development, transportation infrastructure, and flood control projects. The river’s course is paralleled by the Saw Mill River Parkway for much of the river’s length. Construction of the parkway entailed moving a portion of the river channel, as well as co-construction of a trunk sewer line leading to Westchester County’s largest wastewater treatment plant, in Yonkers.

The river has suffered the impacts of flood control projects including straightening, relocating, and lining of the river channel; filling lowlands; constructing flood walls; and replacing the river channel with a concrete flume. As urban Yonkers grew, extensive sections of the Saw Mill River were completely covered. In 2011, a decade’s work by the Saw Mill River Coalition and Groundwork Hudson Valley culminated in the daylighting of a portion of the Saw Mill River in Yonkers. Additional areas have been daylighted since then.



This program is a partnership of Riverkeeper, Sarah Lawrence College Center for the Urban River at Beczak, and Yonkers Paddling and Rowing Club. It builds on Entero monitoring started in 2011 by the Yonkers Paddling and Rowing Club in partnership with the New York City Water Trail Association and The River Project and modeled on Riverkeeper’s ongoing monitoring projects. It also builds previous water quality research done by Groundwork Hudson Valley, including a comprehensive study of the Saw Mill River watershed from 2008-2012. Testing for fecal indicator bacteria was a major part of the sampling program, and the study resulted in infrastructure improvements in Chappaqua and additional investigations in Yonkers.

Samples are collected by SLC CURB, YPRC, Saunders Trades and Technical School students, Village of Pleasantville CAC, Saw Mill River Coalition, and local residents. Samples are processed in SLC CURB’s lab in Yonkers.

Sampling in this watershed in 2017 was funded by an EPA Urban Waters Small Grant. Sampling and sample processing procedures are described in the program’s Quality Assurance Project Plan.

For past and current data from the Hudson River and Saw Mill River see: or

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