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Bay and Coastal Waters

Rhode Island’s coastal waters consist of 159 square miles of estuarine and marine shoreline waters. Estuaries constitute transition zones from freshwater to salt water and are considered highly productive ecosystems that provide nursery habitat for important commercial and recreational fisheries. More than 70% of Rhode Island’s recreationally and commercially important finfish species depend on estuaries for a portion of their life cycle.

In the center of Rhode Island lies Narragansett Bay - a temperate, well –mixed estuary covering 147 square miles. This vital natural resource supports a diversity of recreational activities and is integral to our economy including commercial fisheries, tourism, transportation and industry. The Bay and its watershed are shared with Massachusetts.

The major tributary rivers discharging to the Bay include the Blackstone and Pawtuxet Rivers as well as the Taunton River in Massachusetts. Rhode Island’s coastal waters also include Little Narragansett Bay and a number of coastal ponds.

Narragansett Bay – Improvements to Wastewater Treatment

RIDEM regulates and tracks the performance of wastewater treatment facilities (WWTF). As reflected in the findings below, during the last 30 years WWTFs have significantly reduced the discharge of pollutants through advanced treatment and other operational improvements.

Total Nitrogen: The summer season (May – October) nitrogen loads from the eleven RI WWTFs have been reduced 30% in 2006, 54% in 2012 and 73 % in2016 when compared to the (pre-nitrogen reduction) early 2000s time period. Similar reductions have been achieved from six MA WWTFs

Total Residual Chlorine: The amount released from all Rhode Island WWTFs reduced 85% between 1997 and 2001 and has remained between 96% and 98% since. In 2016 only 20.2 lbs/day was discharged, less than 1/10 of the permitted levels.

Effluent Toxicity Testing: From October 2014 - June 2017, Rhode Island WWTFs achieved 93% compliance with the requirement for no chronic (i.e. sub-lethal) effects beyond the mixing zone.

Phosphorus: WWTFs along the Blackstone, Pawtuxet, Taunton, Ten Mile, and Woonasquatucket have been required to reduce phosphorus loads. The annual loads from all 6 Rhode Island WWTFs that discharge to rivers have been reduced 28% in 2004, 71% in 2006 and 85% in 2011 when compared to 2000. Similar reductions have been achieved from Massachusetts WWTFs.

Read/download factsheets with further details about the progress WWTFs have made reducing outputs of Total Residual Chlorine, Nitrogen, Phosphorus, and Metals:

Office of Water Resources
235 Promenade Street
Providence, RI 02908-5767
Phone: (401) 222-3961