The short version
In 1998 the Rhode Island Department of Environmental Management took stock of Narragansett Bay after 25 years of the Clean Water Act. Upgraded sewage treatment plants had sharply reduced the organic waste that once caused fish kills, and controls on industry had cut metals. But nitrogen was a different story. Even good secondary treatment doesn’t remove it, and septic systems in growing suburbs were adding more. The report also tells how one cove, Greenwich Bay, was brought back to shellfishing.
What the researchers did
The report was prepared for the Governor’s Advisory Council on the Environment as a plain-language “state of the environment” summary. It draws on monitoring data, treatment plant records and University of Rhode Island research.
- It tracked four kinds of pollution: organic waste, metals, disease-causing organisms and nutrients.
- It separated “point sources,” such as treatment plant pipes, from scattered “non-point” sources, such as septic systems, lawns and runoff.
- It used long-term records, including treatment plant discharges back to the 1950s and salt marsh sediment cores that record pollution over centuries.
What they found
- Sewage treatment worked for organic waste. After decades of upgrades, the upper-bay treatment plants were removing 90% to 97% of the oxygen-consuming organic load.
- Nitrogen was not under control. URI scientists estimated that people had increased nitrogen loading to the bay five-fold since before colonization, probably doubling algae production. Rivers carried 62% of measurable nitrogen inputs, treatment plants on the bay 28%, runoff 6% and rain and snow 5%.
- Septic systems were a growing concern. The report warns that failing septic systems
can contribute significantly to nutrient-loading
(RIDEM, 1998) and that even working conventional systems do little to cut nitrogen. It suggests nitrogen-reducing septic systems may be needed near the bay. - Combined sewers were the biggest bacteria source. Combined sewer overflows supplied about 92% of the bacteria from major point sources, and about 19% of the bay’s shellfish beds were permanently closed.
- A local success. Greenwich Bay, which supplied nearly 90% of the bay’s winter shellfish harvest, closed in 1992 because of bacteria. Agencies, URI, advocacy groups and volunteer monitors found the sources. Fixes included improvements at a farm, new sewers and alternative septic systems where there were no sewers, and the bay reopened to shellfishing.
What it means for Waquoit Bay today
Narragansett Bay’s history shows that clean water laws and steady investment work, but that nitrogen from homes is the hardest problem to solve. That is exactly the situation in Waquoit Bay, where most of the nitrogen comes from septic systems rather than a treatment plant pipe. The report’s call for nitrogen-reducing septic systems in unsewered areas anticipated the options Cape towns are weighing today.
The Greenwich Bay story is also encouraging for groups like CPWB. Volunteer water quality monitors were part of the coalition that tracked down the pollution sources, and a mix of sewers and alternative septic systems got the job done. The report credits much of the progress to the stewardship of people who live and work in the watershed.
Read the report
Rhode Island Department of Environmental Management. (1998). Narragansett Bay Water Quality: Status and Trends. Prepared for the Governor’s Advisory Council on the Environment, July 1998. No DOI. Official copy: dem.ri.gov.
License: Published by the Rhode Island Department of Environmental Management. No license is stated, so we link to the official state copy rather than hosting it here.
Drafted with AI assistance from the linked source.
