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Water Monitoring and Assessments


PRWC is one of a number of volunteer groups statewide who contribute water quality data to the Connecticut Department of Energy and Environmental Protection (DEEP).  DEEP is mandated by the Federal Clean Water Act to monitor water quality of the State’s rivers and streams. With nearly 6,000 miles of rivers and streams in Connecticut, CT DEEP certainly can’t monitor every stream on its own.  Working together, and following established protocols for monitoring, PRWC and other groups are able collect water quality data to fulfill both state and local monitoring objectives.

Stream assessments within the Pomperaug Watershed support comprehensive evaluation of the physical, chemical and biological characteristics of the watershed in relation to human health, ecological conditions, and designated water uses. Documenting such characteristics will help establish cause-and-effect relationships, evaluate the effectiveness of current and future remediation and restoration activities, provide input for management tools such as models, and support scientifically-based decisions for preserving and improving the quality of our local water resources.


Below is an overview of the monitoring programs PRWC engages in each year.  For a more comprehensive look at water quality conditions in Connecticut, refer to CT DEEP’s most recent Integrated Water Quality Report to Congress.


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.

To view PRWC’s active sampling sites and results for the current two-year monitoring cycle, check out our interactive map.

Stream Temperature Monitoring


The Volunteer Stream Temperature Monitoring Network is Connecticut DEEP’s newest volunteer monitoring program.  Established in 2008 with support from the US EPA volunteer monitoring equipment loan program, the Network includes a growing number of volunteer monitoring organizations across the state.  Participants in the program are trained by DEEP staff to install a stream temperature data logger (programmed to record hourly stream temperature) at local stream sites of interest each spring (April-May), in order to capture data during the critical summer low flow period (June-August). Loggers are retrieved by volunteers in the early fall (September-October) and returned to DEEP for download and data analysis. The data generated by the Volunteer Stream Temperature Monitoring Network volunteers are instrumental to DEEP’s water quality standard development, fish habitat assessment, and potential stream habitat restoration efforts.


Water temperature can be inherently variable as it is influenced by factors including air temperature, riparian characteristics, and groundwater input. Water temperature itself is an important variable in determining the biology of a particular stream segment. This data can be used to complement ongoing watershed efforts to protect/restore aquatic habitat by both understanding water temperature variability and to be able to characterize the type of water temperature habitat (cold, cool, or warm water) of the stream segment.


To view PRWC’s active sampling sites and most recent results, check out our ambient water sampling map. 

Annual Macroinvertebrate Survey

Since 2006, PRWC has conducted annual Macroinvertebrate Surveys following Connecticut DEEP’s protocol for Rapid Bioassessment by Volunteers (RBV).  RBV is a ‘treasure hunt’ during the fall (September through November) for Connecticut’s healthiest streams!  RBV volunteers monitor streams specifically for pollution sensitive Macroinvertebrates – small organisms that spend a large part of their life cycle clinging to the undersides of rocks in river riffles.  If volunteers are able to find four or more of these ‘Most Wanted’ macroinvertebrate types at an RBV location, it can provide DEEP with evidence to document the stream as having excellent water quality - making it one of Connecticut’s healthiest streams! 


The RBV program provides volunteers with a standardized methodology for using aquatic macroinvertebrates to assess the relative water quality of wadeable streams (those that you can walk across).  Aquatic macroinvertebrates are excellent indicators of stream quality not only because they are relatively easy to collect and identify, but because certain species are very sensitive to changes in water quality. The most sensitive species can tolerate only very small amounts pollution and will therefore only be present in Connecticut’s healthiest streams.   


To view PRWC’s active sampling sites and results for the current two-year monitoring cycle, check out our interactive map.

Thermal Monitoring Locations

Recent Bacteria Levels


Safe for a designatedswimming


The Connecticut DEEP's Water Quality Standards lists Escherichia coli (E. coli) as the primary sanitary indicator for fresh water with concentration ranges safe for different uses as specified in the legend.

E. coli, a type of bacteria found abundantly in the gut of mammals including humans, is used as the primary sanitary indicator for fresh water.  High bacteria levels can indicate water quality degradation from pollutant sources such as agricultural runoff, septic contamination, and pet waste. E. coli usually poses little concern to humans with the exception of one strain that is capable of causing illness. Prolonged exposure to or swallowing water containing high levels of E. coli can cause mild to severe symptoms that may present in a way similar to a stomach virus, an ear infection or a rash. Typical recovery is expected within a few days to over a week.

The E. coli bacteria levels for different types of recreation are determined by the number of Colony Forming Units / 100 ml (CFU/100ml).  Results from the water testing lab are reported as Most Probably Number (MPN/100ml).  


Safe for non-designated swimming areas


Safe for boating, fishing or other recreational uses, not including swimming.


Not safe for swimming, boating, fishing or other recreation





Thermal Map
Bacteria Map
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