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The Blackstone River

By Meg Kerr

The Blackstone River begins in Worcester, Massachusetts at the confluence of the Middle River and Mill Brook.  It flows southward until it flows over the Slater Mill falls into the Seekonk River at the head of Narragansett Bay.  The Blackstone River's average flow is about 862 cubic feet per second and it drains an area of 472 square miles, about one-third the size of Rhode Island.  The majority of the drainage area (373 square miles) is in Massachusetts.

The main tributaries of the Blackstone are Kettle Brook and the Quinsigamond, Mumford, and West rivers in Massachusetts; and the Mill, Peters, and Branch rivers in Rhode Island.


The Blackstone River has been a part of American history since 1635 when the first English settlement in Rhode Island was established by William Blackstone in the Blackstone Valley.  The valley quickly attracted other settlers and by the late 1700s, many communities were located on the river near small water-powered grist mills.   Industrial development along the Blackstone changed dramatically after 1793, when Samuel Slater opened Slater Mill, the first cotton mill in the United States to use mechanical spinning machines.  After the mill opened, water-power sites along the Blackstone developed rapidly.  By 1800, the town of Pawtucket supported 29 cotton mills.  Mill villages like Woonsocket, Blackstone, Millville, Uxbridge, and Millbury grew up all along the river.  By the 1830s, there was one dam for every mile of river along the main stem and tributaries.

Transportation from industry to market was often a problem.  In 1792, John Brown suggested that a canal be constructed along the Blackstone linking Providence with Worcester.  Opposition was voiced by mill owners, who feared that the canal diversion would interfere with their hydropower, and farmers, who feared increased competition for water from urban areas.  In 1823, the project was funded by both the Massachusetts and Rhode Island legislatures.  The canal, 35 feet wide at the top, 18 feet wide at the bottom and 4 to 6 feet deep, was constructed by hand.  It was 45 miles long, including 45 locks and a system of reservoirs.  The canal opened in 1828, but existed only briefly before closing in 1849, two years after the Providence and Worcester Railroad opened. 

Financial problems plagued the canal from the start, as did structural failures and a fluctuating water level.  In addition, the Blackstone Canal Company faced continuing legal challenges from mill owners, who asserted that their revenues were affected by the canal's operation.

By the late 1800s, the Blackstone Valley included mills that produced cotton thread and wool and cotton cloth, factories that dyed material, and factories that manufactured the textile-producing machinery.  The valley also supported companies that manufactured  rubber, hats, and wire.  The river supplied these plants with hydropower and water for their manufacturing processes.  It also became a convenient site for disposing of industrial waste and sewage from the ever-expanding population of the valley.

By the early 1900s, the upper Blackstone River in Massachusetts was grossly polluted.   In a report to the state legislature, the Massachusetts Department of Health stated, "The Department finds that the condition of the Blackstone River is offensive throughout its course, from Worcester to the state line at Blackstone.  The condition of the stream is likely to grow worse until effective measures are completed for removing from the river much of the pollution which it now receives."

In 1922, Gage and McGouldrick, investigating the pollution of certain Rhode Island waters, reported on the condition of the Blackstone in Rhode Island.  They found that the dissolved oxygen concentrations at the mouth of the Blackstone River were at levels characteristic of clean water.  They concluded that the river was clean as it entered tidal waters in the Seekonk River.  However, it is likely that their measurements were affected by re-aeration, as the river flowed over the Slater Mill dam.

The intense industrial usage of the Blackstone left a legacy of pollution.   Textile manufacturers discharged dyes, leather and metal-working plants discharged heavy metals, and wood-working companies discharged varnish, solvents, and paints.   Many of these pollutants can still be found in the river's sediments today, over 100 years after they were released.  These pollutants continue to influence water quality and overall health of the Blackstone River's ecosystem.

During the early 1900s, the textile industry that supported much of the Blackstone River Valley began to fold.  Southern mills, which had produced only 6 percent of the nation's cotton in in 1880, were successfully competing with mills in the Northeast.   By 1923, half of the nation's cotton was produced in the South.  Between 1920 and 1980, most of the Blackstone Valley's cotton mills closed and 90 percent of the woolen and worsted mills were shut down.  The valley lost population, and in 1971 the Blackstone River was labeled "one of America's most polluted rivers" by an article in Audubon magazine.

Current Water Quality

Today (1990), the Blackstone River, from the Massachusetts border to the falls at Pawtucket, is classified as class C, suitable only for boating and other secondary contact recreation, fish and wildlife habitat, and industrial processing and cooling.  The Peters and Mill rivers are classified as B waters, suitable for public water supply with suitable treatment, agricultural use, bathing, and other primary contact recreational activities, and fish and wildlife habitat.  The Branch River is classified as C above Slatersville Reservoir, and B through the reservoir to its confluence with the Blackstone.

The water quality of the Blackstone River continues to be affected by sewage discharges, combined sewer overflows, urban and agricultural runoff, and leaching from active and abandoned landfills.  At its mouth, the Blackstone shows high concentrations of many pollutants.  This pollution, combined with the large flow of the river, makes the Blackstone the major riverine source of oxygen-consuming materials (BOD), fecal coliform bacteria, nitrogen, polychlorinated biphenyls (PCBs), petroleum hydrocarbons (PHCs), and many metals (cadmium, copper, nickel, chromium, lead) to upper Narragansett Bay.

The Upper Blackstone Water Pollution Abatement District (UBWPAD) wastewater treatment facility in Worcester is the largest source of pollution entering the Blackstone in Massachusetts.  The Blackstone is a small river when it flows through Worcester, providing minimal dilution for domestic and industrial discharges from the city.  In the summer, the plant's discharge of 56 million gallons a day can actually exceed the flow of the river.

Though the UBWPAD plant does an exemplary job removing conventional, oxygen-consuming materials from the wastewater, it is not as effective in treating toxic wastes received from industrial discharges.  The plant accounts for 77 to 96 percent of the cadmium, copper, chromium, nickel, and zinc, discharged to the Blackstone River in Massachusetts.

The river also receives wastes in Rhode Island, including discharges from the city of Woonsocket, and wastes from industries producing batteries, insulated wire and cable, and blown glassware.  Sewer overflows from the Blackstone Valley District Commission collection system can have serious effects on the river's water quality in wet weather.

In 1988, the state of Massachusetts reported to Congress that all of the river was polluted and not suitable for bathing.  In Rhode Island, the entire 16 miles of river was not suitable for boating and other secondary contact recreation, as fish and wildlife habitat, or as industrial water supply.

Protection of the Blackstone River Corridor

During the early 1970s, citizens interested in restoring the Blackstone's waters and adjacent lands formed the Blackstone River Watershed Association.  This organization, and other groups in the Blackstone Valley, lobbied for parkland development  along the river in Massachusetts and Rhode Island.  Massachusetts designated the Blackstone River and Canal Heritage State Park, a linear park extending from Worcester to the Rhode Island border.  In 1983, Rhode Island formed the Blackstone River State Park along a three-mile segment of the Blackstone canal and towpath.  This park has now grown to include 150 acres in Lincoln and Cumberland.

In 1986, the Blackstone River Valley National Heritage Corridor was established by Congress to preserve and interpret the significant historic and cultural lands, waterways, and structures within the valley.   The National Park Service is working with Rhode Island and Massachusetts to pursue park development along the River and to coordinate a valley-wide land use strategy.

In Rhode Island, the Department of Environmental Management is developing a greenway along the Blackstone between the villages of Albion and Berkley.  A bikeway is also under development, which will ultimately extend from India Point Park in Providence west to North Smithfield and east to Bristol.

For further reading:

Metal Inputs to Narragansett Bay: A History and Assessment of
Recent Conditions
pdf (Sea Grant)
Blackstone River (EPA)

Printed 1990

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