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Bacteria and Nitrate Monitoring


PRWC launched a bacteria and nitrate monitoring program in 2019. Nitrogen is an indicator of fertilizer runoff, septic failure, and animal waste. Nitrogen is also a contaminant of major concern for Long Island Sound (fed by all the rivers and streams throughout Connecticut). Sampling for nitrate provides a screening level indicator for total nitrogen. Bacteria are an indicator of general water quality degradation from septic effluent and agricultural runoff, which are the principle sources of contamination in the Pomperaug River.

The goal of PRWC’s bacteria and nitrate monitoring is to establish an improved baseline of water quality conditions near sites targeted for the future implementation of best management practices (BMP) identified in the Watershed Based Plan. The Plan addresses stream impairments identified in DEEP’s Biannual Water Quality Report to Congress through the implementation of BMPs designed to reduce non-point source pollutant loading to the Pomperaug River and its tributaries.

By sampling for E. coli bacteria and nitrate, PRWC will be able to further characterize pollutant sources and problem areas, and further bracket priority areas for non-point source pollution and stormwater runoff reduction projects. The data will also help differentiate sources of contamination in the river.

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NOTE:  Indicator bacteria levels can change dramatically from day to day. Therefore, this information is a snapshot of river conditions at the moment the sample was taken.  To best understand the water cleanliness in terms supporting safe recreation, open each sample location’s page for more detail and historical data showing trends in water cleanliness. Be sure to take the most recent sample date into account as well as patterns over time, recent weather, and flow conditions when deciding whether to swim, wade, fish, or boat.  You can also view these data by turning the various layers on and off for each sampling event.  The layer turned on highest up in the list of layers available will the one visible. 

In general, bacteria levels are typically elevated during and shortly after precipitation events (wet weather).  Good precautions to take include:

  • Avoid swimming right after a rain storm where runoff is generated (> 0.1" rain)

  • Avoid contact with the river downstream of a sewage discharge

  • Cover open cuts, use ear and nose plugs

  • Wash hands before eating or drinking

Also remember, rivers are inherently risky environments for recreation due to variable streamflow (velocity), depth, substrate, and other hazards.  Always be sure to share your recreation plan before you go out in/on the water.

We wish you a fun and safe season enjoying your rivers!


(>235 to 575 CFU / 100 mL)

Safe for Boating & Fishing (minimal water contact);
Not safe for Swimming

This map shows locations tested for Escherichia coli (E. coli) bacteria. Users can click on the site to view more information about the monitoring location, including stream name, description of the site, town, as well as the bacteria, nitrate, and conductivity level at the time the water sample was collected.  E. coli data are reported as "colony forming units per 100 mL" of water (or CFU / 100mL)

The different colored icons and bacteria ranges represent risk thresholds, which are based on the statistical chances of getting sick if you come in contact with water in these bacteria ranges. We test for E. coli, a bacterium that is found in the guts of all warm-blooded animals, including humans. Most E. coli will not cause illness. We test for E. coli because it is often an indicator for the presence of other, more difficult to test for pathogens that may cause waterborne illnesses to those swimming, wading, or boating.

Here's how to interpret the data presented:


(>575 CFU / 100 mL)

Unsafe for Swimming, Boating, Fishing, Wading 


(0 to 235 CFU / 100 mL)

Safe for Swimming, Boating, Fishing, and Wading


Monitoring Sites


East Spring Brook, Nonnewaug Road, Bethlehem

Nonnewaug River, Route 47 Bridge, Washington Road, Woodbury

Nonnewaug River, USGS Gauge, Mill Road, Woodbury

Pomperaug River, USGS Gauge, Ewald Park, Poverty Road, Southbury

Pomperaug River, Audubon Center at the Bent of River, Southbury

Pomperaug River, 195 Flood Bridge Road, Southbury

Pomperaug River, Oakdale Manor Road, Southbury

Pomperaug River, Heritage Village River Gardens at Winship Drive, Southbury

Pomperaug River, Middle Quarter, South Pomperaug Avenue, Woodbury

Transylvania Brook, Seman Park, East Flat Hill Road, Southbury

Weekeepeemee River, Mill Pond Road, Bethlehem

Weekeepeemee River, Crane Hollow Road, Bethlehem

Weekeepeemee River, Jack's Bridge Road, Woodbury

Weekeepeemee River, Brushy Hill Road, Woodbury

Weekeepeemee River, Chohees Trail, Woodbury

Monitoring Protocols

Summary of Findings (2019 to 2022)

Thermal Map
Bacteria Map
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