Rhode Island’s estuaries connect a large inland watershed with a changing coastal environment. The Narragansett Bay estuary proper covers 196 square miles, while the smaller Little Narragansett Bay estuary proper covers 4.8 square miles. Together, the measurements below show the scale of these waters, the communities and habitats connected to them, and the pressures documented across different measurement periods.
Contents
- Narragansett Bay at a glance
- Little Narragansett Bay at a glance
- Water quality and aquatic life
- Wetlands, seagrass, and habitat
- Rainfall, sea level, and climate exposure
- Wastewater and community susceptibility
- Land cover, development, and protection
Narragansett Bay at a glance
The main bay is a large estuarine system with a broad geographic reach. According to NBEP Quick Facts, Narragansett Bay’s estuary proper covers 196 square miles and has 563 miles of salty shoreline, including islands. Its maximum depth is 194 feet near Newport.
The surrounding watershed is much larger than the open estuary. It covers 1,705 square miles and reaches a maximum elevation of 1,388 feet near Worcester. The watershed includes 71 towns and cities in Massachusetts and 34 towns and cities in Rhode Island, for a total of 105 communities identified in the source.
The watershed population is 1.95 million people. Its freshwater network includes 3,578 miles of streams and rivers. These figures help distinguish the bay itself from the much larger land area and population that influence its water and shoreline.
| Narragansett Bay measure | Reported figure | Measurement context |
|---|---|---|
| Estuary proper | 196 square miles | NBEP Quick Facts |
| Salty shoreline | 563 miles | Includes islands |
| Maximum depth | 194 feet | Near Newport |
| Watershed area | 1,705 square miles | NBEP Quick Facts |
| Watershed population | 1.95 million | NBEP Quick Facts |
| Streams and rivers | 3,578 miles | Watershed total |
Little Narragansett Bay at a glance
Little Narragansett Bay is smaller in area but still linked to a substantial watershed. NBEP Quick Facts reports 4.8 square miles for the estuary proper and 37 miles of salty shoreline, including islands. Its watershed covers 317 square miles, reaches a maximum elevation of 673 feet in West Greenwich, and has 78 thousand residents.
The watershed includes 4 towns in Connecticut and 9 in Rhode Island. Its streams and rivers total 521 miles. In 2012, 605 acres of salt marsh were observed. In 2016, 96 acres of seagrasses were observed, down from 201 acres in 2012.
The two systems differ substantially in scale, as shown by the source measurements:
| Measure | Narragansett Bay | Little Narragansett Bay |
|---|---|---|
| Estuary proper | 196 square miles | 4.8 square miles |
| Salty shoreline | 563 miles | 37 miles |
| Watershed area | 1,705 square miles | 317 square miles |
| Watershed population | 1.95 million | 78 thousand |
| Streams and rivers | 3,578 miles | 521 miles |
The smaller estuary is also subject to a clear access and use constraint: 100% of Little Narragansett Bay is closed to shellfishing. The watershed has 11 public access points to the shore, according to NBEP Quick Facts.
Water quality and aquatic life
Narragansett Bay’s nutrient measures show improvement alongside remaining condition gaps. Since 2000, nitrogen entering Narragansett Bay has been reduced by 55%, while total phosphorus entering the bay has been reduced by 42%. These are changes measured from the 2000 baseline, not current annual totals.
The aquatic-life assessment reported in NBEP Quick Facts was not uniformly healthy. As of 2014, just half of the estuarine waters assessed for Narragansett Bay were in healthy condition for fish and other aquatic life. About one quarter of the estuary remained unassessed for aquatic-life condition.
The Little Narragansett Bay watershed figures separate streams and rivers from ponds and lakes, and separate aquatic wildlife from recreation. In the Rhode Island portion, 28% of assessed streams and rivers were impacted for aquatic wildlife, while 11% of streams and rivers remained unassessed for that use. Among assessed ponds and lakes, 73% were fit for aquatic wildlife and 10% were impacted by excess nutrients and oxygen depletion; another 15% remained unassessed.
Recreation results present a different pattern. In the Rhode Island portion of the Little Narragansett Bay watershed, 60% of assessed streams and rivers were fit for recreation, while 40% were impacted by bacterial pollution for recreation use. Ten percent of streams and rivers remained unassessed for recreation. Among assessed ponds and lakes, 100% were fit for recreation, and 4% remained unassessed.
Wetlands, seagrass, and habitat
Salt marsh is a major measured habitat in both systems. Narragansett Bay had 3,371 acres of salt marsh mapped in 2012. More than 50% of Narragansett Bay salt marshes were lost from the 1800s to the 1970s, a historical change reported by NBEP Quick Facts rather than a present-day estimate.
Little Narragansett Bay had 605 acres of salt marsh observed in 2012. Its seagrass observations show a shorter-term decline: 201 acres in 2012 compared with 96 acres in 2016. Because the observations come from different years, the figures describe a change between those survey dates rather than a current inventory.
Habitat condition in Narragansett Bay was also tracked at sampling sites. From 2008 to 2018, habitat at 80% of sampling sites improved or maintained good quality. In 2018, intermediate and mature benthic communities were found at 71% of sites. These percentages describe sampling-site results and should not be read as a complete condition rating for every part of the estuary.
Sea-level scenarios indicate potential future pressure on mapped marsh. An estimated 13% to 87% of mapped salt marsh could be submerged under 1-foot and 5-foot sea-level-rise scenarios. The range reflects the two scenarios reported in NBEP Quick Facts, not a single forecast of realized loss.
Rainfall, sea level, and climate exposure
Long-term observations in the Narragansett Bay region show changing rainfall and water levels. Average annual rainfall increased by 0.4 to 0.7 inches per decade since 1895. Intense-storm rainfall volumes increased 71% since 1965.
At the Newport tide gauge, sea level rose 9 inches from 1930 to 2017. Climate models project another 9 to 11 feet of sea-level rise by 2100 for the region. The historical tide-gauge figure is an observed change through 2017; the 2100 figures are model projections and should not be treated as measured sea-level change.
These dates matter when comparing the numbers. The rainfall trends use long historical periods beginning in 1895 and 1965, the Newport tide-gauge measurement ends in 2017, and the additional 9-to-11-foot range extends to a projected 2100 horizon. They describe different kinds of evidence and different time windows.
Wastewater and community susceptibility
Wastewater infrastructure is one of the watershed-scale measurements reported by NBEP Quick Facts. The Narragansett Bay watershed has 37 wastewater treatment plants. Together, those plants discharge about 203 million gallons per day of treated wastewater and serve approximately 62% of the watershed population.
The figures are estimates where the source uses approximate language: 203 million gallons per day is reported as “about,” and the population served is reported as “approximately” 62%. They therefore indicate infrastructure scale without supporting a more precise calculation of per-person discharge or service coverage.
Susceptibility is also distributed across communities. Sixty-five percent of towns in the region have populations above the 80th percentile of higher susceptibility. This is a regional susceptibility statistic, not a statement that 65% of residents or 65% of land area falls into that category.
Land cover, development, and protection
The Little Narragansett Bay watershed’s land-cover measures show a predominantly forested but changing landscape. NBEP Quick Facts reports that the watershed is 61% forested and 11% developed. Overall impervious cover is less than 5%.
Since 2001, the watershed lost 1.4% of forests and gained 3.5% developed lands. Those are land-cover changes over the period beginning in 2001, while the 61%, 11%, and less-than-5% figures describe the reported watershed composition rather than the same change interval.
Impervious cover varies within the Rhode Island subwatersheds. Most Rhode Island subwatersheds in the Little Narragansett Bay area fall below 7% impervious cover, except the Lower Pawcatuck River watershed at 31% impervious cover. The exception shows why the watershed-wide “less than 5%” figure should not be applied to every individual subwatershed.
Population and protection have changed alongside land cover. The Little Narragansett Bay watershed population grew 21.5% since 1990. Rhode Island has protected 33% of the Little Narragansett Bay watershed, or nearly 60,000 acres. The protected-area figure is reported as both a percentage and an approximate acreage total, while the population growth figure uses 1990 as its baseline.
Taken together, these statistics describe estuaries with large connected watersheds, measurable nutrient reductions, uneven aquatic-life assessments, changing habitat, and exposure to long-term climate and development pressures. The observations belong to their stated years and geographies: Narragansett Bay, Little Narragansett Bay, the Rhode Island portion of the smaller watershed, or the wider region.