Narragansett Bay is a large estuary connected to a watershed that crosses Rhode Island and Massachusetts and links communities, rivers, wetlands, lakes, forests, and developed land. The figures below describe its physical scale, human history and settlement patterns, environmental conditions, and current conservation priorities. Dates and geographic boundaries matter: some measurements describe the bay itself, while others describe the wider watershed or the broader Narragansett Bay region.
Contents
- At a glance
- The bay and its watershed
- People, communities, and development
- Land cover and protected places
- Habitats and sea-level exposure
- Water quality and public uses
- Rivers, dams, and restoration
At a glance
The following figures provide a compact scale comparison. They come from different reports and use slightly different geographic definitions, so they should not be treated as interchangeable totals.
| Measure | Figure | Source and period |
|---|---|---|
| Bay water volume | Over 700 billion gallons | RI DEM, Introduction to Narragansett Bay |
| Bay area | 150 square miles | RI DEM, Introduction to Narragansett Bay |
| Watershed area | 1,705 square miles | 2025 NBEP CCMP Update |
| Bay portion associated with that watershed | 196 square miles | 2025 NBEP CCMP Update |
| Watershed residents | About 2 million people | 2025 NBEP CCMP Update |
| Communities and states | 113 communities in three states | 2025 NBEP CCMP Update |
| Salt marsh habitat | Roughly 4,300 acres | 2025 NBEP CCMP Update |
| Seagrass habitat | 875 acres | 2025 NBEP CCMP Update |
The RI DEM Introduction to Narragansett Bay describes a watershed of about 2,000 square miles, with about 60% in Massachusetts and 40% in Rhode Island. It also describes more than two million residents and more than ten million tourists visiting the bay each year. The 2025 NBEP CCMP Update uses a 1,705-square-mile watershed boundary and identifies a 196-square-mile bay portion associated with it. These differences reflect reporting boundaries rather than a single precise number that applies to every study.
The bay and its watershed
The bay holds over 700 billion gallons of water across 150 square miles, according to RI DEM’s Introduction to Narragansett Bay. The surrounding watershed includes more than 3,500 miles of streams and rivers, according to the 2017 State of Narragansett Bay and Its Watershed Summary Report. The 2025 NBEP CCMP Update gives a broader regional figure of more than 4,000 miles of rivers and streams, along with over 40,000 acres of lakes and ponds.
The watershed is organized around major river systems. The 2025 NBEP CCMP Update identifies the Blackstone River, Taunton River, and Pawtuxet River as feeders of the bay watershed. The same update describes the bay as extending more than 50 miles inland in the region and says the wider region spans over 2,000 square miles of land across three watersheds.
Population figures also vary by report and year. The 2017 summary report describes 1.95 million people living in the watershed and gives an approximate population of 1.9 million in 2014. Its population comparison shows an 8% increase between 1990 and 2010. The 2025 NBEP CCMP Update describes two million people across 113 communities in three states. The RI DEM introduction uses the broader wording “more than two million residents.”
The region is therefore both a physical system and a lived landscape. Its scale includes a 150-square-mile bay, a watershed measured at 1,705 square miles in the 2025 update, and a larger regional description covering more than 2,000 square miles of land. Each boundary helps explain a different part of the bay’s local history and environmental story.
People, communities, and development
Settlement has changed the amount and pattern of developed land in the watershed. The 2017 summary report measured average developed land per person at 1.8 acres in 1990 and 2.1 acres in 2010. It characterizes that change as a 16% increase in developed land per capita. Some areas reached 3.9 acres of developed land per person in 2010.
The same report found that 35% of the watershed was urban and 39% was forested in 2011. Between 2001 and 2011, forest land declined by 4%, while urban land increased by 8.5%. Coastal subwatersheds were 65% to 85% urban in 2011, while headwater subwatersheds were about 70% forested.
The NBEP Quick Facts provide a later land-cover snapshot. In 2016, the watershed was 42% forested and 34% developed. Some coastal areas were as much as 86% developed. From 2001 to 2016, forests declined by 6% and developed lands increased by 10%. Parts of the Taunton River area saw up to 21% developed-land expansion since 2001.
| Indicator | Earlier measure | Later measure |
|---|---|---|
| Forest cover | 39% in 2011 | 42% in 2016 |
| Developed cover | 35% urban in 2011 | 34% developed in 2016 |
| Forest change | 4% decline, 2001–2011 | 6% decline, 2001–2016 |
| Developed-land change | 8.5% increase, 2001–2011 | 10% increase, 2001–2016 |
These percentages come from different source reports and land-cover classifications. They are useful as dated snapshots, but they do not establish a single continuous trend without a common methodology.
Infrastructure is another connection between population and water. The 2017 summary report says 62% of watershed residents were served by sewer systems, while 38% used septic systems and cesspools. NBEP Quick Facts identify 37 sewage treatment plants discharging approximately 203 million gallons per day and serving approximately 62% of the watershed population.
Impervious land cover is a measure of built surfaces that limit infiltration. The 2017 summary report estimated 14% impervious cover across the entire watershed, with 36 of 52 subwatersheds exceeding the 10% threshold. NBEP Quick Facts likewise report that 36 of 52 subwatersheds exceeded 10% impervious cover and that immediate coastal lands draining to the bay were 20% impervious.
Land cover and protected places
Protection has preserved substantial portions of the watershed, while large areas remain exposed to future change. As of 2015, the 2017 summary report counted 171,244 acres of natural land protected as open space. Those protected lands represented more than 15% of the watershed’s land, and 83,561 protected acres had high ecological integrity.
The same report counted more than 450,000 acres of natural land that remained unprotected, representing 41% of the watershed. Of that unprotected total, 185,233 acres had high ecological integrity. In two named river portions, the imbalance was especially pronounced: the Mount Hope River portion had an unprotected-to-protected ecologically significant land ratio of 20:1, and the Segreganset River portion had a ratio of 18:1.
NBEP Quick Facts give a later summary in which over 17% of watershed land, or about 180,000 acres, had been protected. Nearly 455,000 acres of undeveloped land remained unprotected, and over 17% of watershed lands with high ecological integrity remained unprotected. The 2025 NBEP CCMP Update describes the broader Narragansett Bay region as encompassing more than one million acres, including about 200,000 acres of protected open space.
The figures use different dates and geographic scopes. The 2015 acreage, the later NBEP watershed summary, and the 2025 regional total should be read as separate historical and planning snapshots. Together, they show both an established conservation network and a large remaining inventory of natural or undeveloped land.
Habitats and sea-level exposure
Salt marshes and seagrasses are two of the bay’s measured coastal habitats. NBEP Quick Facts report that 3,371 acres of salt marsh were mapped in the bay in 2012. Under NBEP’s sea-level-rise projections, an estimated 13% to 87% of those salt-marsh acres could become submerged under one-foot and five-foot projections, respectively. These are projections, not observations of completed submergence.
The same source records 479 acres of seagrasses observed in the bay in 2016. The 2025 NBEP CCMP Update gives a broader regional figure of roughly 4,300 acres of salt marsh habitat and 875 acres of seagrass habitat. Because the two sources use different dates and geographic descriptions, the 2012 and 2016 habitat observations should not be directly subtracted from the 2025 regional figures.
The scale of the surrounding freshwater landscape is also notable. The 2025 update lists over 40,000 acres of lakes and ponds in the region. The 2017 summary report separately found more than 4,800 acres of ponds and lakes unacceptable for aquatic life in state assessments. Those measurements describe condition, not total habitat area.
Water quality and public uses
State assessments summarized in the 2017 report found 162 miles of streams unacceptable for aquatic life, 57 square miles of estuarine waters unacceptable for aquatic life, and more than 4,800 acres of ponds and lakes unacceptable for aquatic life.
NBEP Quick Facts add percentage-based assessments. Nearly one quarter of assessed freshwater streams and rivers were impacted by excess nutrients and oxygen depletion, including the entire Blackstone River. Another 25% of assessed freshwater streams and rivers were unhealthy for fish and wildlife for other reasons. Nearly 40% remained unassessed for aquatic-wildlife conditions.
For ponds and lakes, 75% of assessed waters were unhealthy for fish and aquatic wildlife. Twenty-five percent were impacted by excess nutrients and oxygen depletion, while 50% were unhealthy for other reasons. Nearly 72% remained unassessed for aquatic-wildlife conditions.
Recreation results were different across water types. More than 60% of assessed freshwater streams and rivers were not suitable for recreation, with up to 80% unsuitable in the Taunton River watershed and coastal areas around the bay. More than 40% of freshwater streams and rivers remained unassessed for recreational use. By contrast, just 2% of assessed freshwater ponds and lakes were not suitable for recreation, while around 50% remained unassessed.
For the bay itself, NBEP Quick Facts report that 85% of the bay was fit for recreation as of 2014, with about 5% unassessed. In 2015, 63% of shellfishing areas were open. Open shellfishing acreage increased by 3,711 acres in the upper estuary in 2017. The bay had 338 public access points to the shore, and about 20% of them, or 70 sites, had never been restricted or impaired for recreation.
Rivers, dams, and restoration
The 2025 NBEP CCMP Update identifies more than 1,000 dams in the Narragansett Bay region. Dams affect how fish move between the bay and upstream habitat, making passage projects a measurable part of restoration planning.
The update highlights a Lower Blackstone Fish Passage Project involving four dams. The project covers 206 acres of spawning nursery habitat and is projected to generate over 200,000 adult spawning river herring per year and 10,000 adult spawning shad per year. Those are projections associated with the project, not counts of fish already produced.
NBEP allocated over $500,000 in Bipartisan Infrastructure Law funds to what the 2025 update describes as the largest fish passage project in the watershed to date. The update also gives one estimate that every mile of river opened to fish passage can contribute more than $500,000 in economic and social benefits.
Taken together, these statistics connect Narragansett Bay’s heritage to its working landscape: rivers that carry water into the estuary, communities built around shorelines and headwaters, habitats measured in acres, and restoration decisions shaped by both ecological conditions and public access.