While there is much scientific debate about the impact of nitrogen from wastewater pollution on the environment of Narragansett Bay, there is no question that the nearly two million people living in the Bay watershed contribute hundreds of tons of nitrogen to the upper Bay annually by way of about 25 wastewater treatment plants in Rhode Island and Massachusetts. Heavy nitrogen loads can have profound effects on estuarine ecosystems. For Narragansett Bay, excessive nitrogen levels are considered one of the primary drivers of hypoxia, or low levels of dissolved oxygen, which occur in summer and occasionally cause fish kills, but have a much more profound influence over which organisms can live on the bottom during summer months. Since 1999, the Narragansett Bay Estuary Program has worked with BrownUniversity, URI and RIDEM to survey summer oxygen levels in upper-mid Narragansett Bay, finding that summer conditions often fall below levels needed to sustain sensitive marine life. In August, 2003, low oxygen levels caused a major kill of menhaden in Greenwich Bay, on the west side of Narragansett Bay.

Nitrogen loads to Narragansett Bay have also changed the very structure of bottom habitats in some areas. Eelgrass, an underwater grass, was once distributed throughout the shallows of Narragansett Bay, providing valuable nursery habitat for bay scallops, flounder and many other creatures. Today, eelgrass in the Bay is limited to a fraction of its historic range, and grows only in the clearer waters of the middle and lower Bay. In the upper Bay, it has been largely replaced by drift seaweed (macroalgae), which thrives in shallow, nutrient-rich waters. The drift macroalgae tends to wash up along the shore of the lower Providence River and Conimicut Point area, where it gives off hydrogen sulfide gas in late summer as it rots in the warm sun, annoying residents with its noxious odor.

Toxic metals, insecticides and other poisonous compounds were formerly a major source of pollution to Narragansett Bay, as with all other urbanized U.S. estuaries. Due to modern discharge regulations, improved wastewater pretreatment, and the decline of Northeastern manufacturing, these inputs have greatly decreased, although may of these contaminants can still be found in the sediments or mud of the rivers and upper Bay, where they create problems for fish consumption as well as management challenges, for example as relates to dredging and dam removal. Storm water and road runoff are now the greatest sources of toxics and a major source of bacteria to Narragansett Bay, carrying chemicals and bacteria washed off the land into the Bay, locally impacting sediments and closing beaches and shellfish beds. A common class of contaminants which has recently emerged as a potential concern in fresh and salt water are pharmaceuticals, which can serve as endocrine disrupters, interfering with the ability of fish and wildlife to successfully reproduce. Little is known about these compounds in the Narragansett Bay Watershed Ecosystem.

Click on the links below to navigate through this section.