Water Quality Testing


Sometimes, we can tell something is wrong with our water just by looking at it. Other times, we simply smell trouble. But most of the problems in our waters—which may be caused by leaky septics, boat discharges, or surface runoff—are not that easily detected. That’s why, since 2008, CUSH volunteers have been collecting water samples in a systematic, long-term project that monitors the water quality of Stonington and Mystic Harbors, the Mystic River, Pequotsepos and Wequetequock Coves, and the major freshwater streams that feed them.

The good news: Near-shore areas that are well flushed by incoming tides, including Stonington and Mystic Harbors, have good to fair water quality. Less-good news: Those tide-flushed pollutants are carried to western Long Island Sound, and in coves where tidal flushing is minimal, water quality is poor. In general, water quality is poorest where water flow is slowest.

Monitoring is critical to understanding and improving the health of our local waters. Using methods developed by the University of Rhode Island’s Watershed Watch, our volunteer citizen scientists are trained to test for dissolved oxygen, salinity, nitrogen and phosphorus, chlorophyll, fecal coliform, and other indicators. Those results are then formulated into a single Aquatic Health Index, a useful water-quality score developed by the Buzzards Bay Coalition in Massachusetts.

We share our data with state and local officials as well as regional environmental organizations and the general public. Long-term monitoring can reveal the biggest pollution challenges and help identify how to fix them. The end result will be not only healthier coves and streams, but a real contribution to a healthier Long Island Sound.


We monitor water quality by collecting water samples and determining their levels of dissolved oxygen, chlorophyll-a (algae), temperature, salinity, turbidity, nutrients (nitrogen and phosphorus), pH, bacteria (enterococci and fecal coliform), and weather conditions.

Stonington Harbor and Wequetequock Cove

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Click on the site icons for specific information, including the site’s Aquatic Health Index (AHI)–a single water-quality score developed by the Buzzard’s Bay Coalition and the Salt Ponds Coalition for New England waters. The AHI is derived from summer levels of oxygen, chlorophyll-a, organic nitrogen, and inorganic nitrogen. If all seven site icons are not visible on this map, click on the [-] button (lower right) then click and hold inside the map and move your mouse down until all the icons appear. Click on an icon to see the site name, description, a photo, and the site’s water-quality summary.


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