WESTPORT, Mass.

Unlike many New England rivers, the one that shares a name with this popular summer town doesn’t have a legacy of industrial pollution buried in its sediment. But despite not being polluted with toxins from long-since-gone jewelry makers and dye manufacturers, the Westport River and its watershed still face the threat of contamination from stormwater runoff, nitrogen-rich fertilizers, failing septic systems and outdated cesspools.

In fact, one of the more commonly seen but often ignored threats — unless you happen to step in it — to this two-pronged river and its economically vital watershed is waste left on the ground by inconsiderate pet owners. While certainly not on the order of concern of, say, carbon pollution, the Environmental Protection Agency (EPA) does label dog waste a “pollutant.”

Sorry, Snoopy, but dog poop is 57 percent more toxic than human waste, according to the EPA, and can harbor bacteria and parasites that cause illness in humans.

This waste problem is so rampant in dog-friendly Westport and the surrounding area that the Westport River Watershed Alliance (WRWA), the nonprofit protector of the this important natural resource, was compelled this year to print a two-fold brochure entitled “The Shocking Truth About Your Dog’s Poop.”

“Even the smallest amount of dog poop is filled with bacteria,” said Roberta Carvalho, the WRWA’s science director.

It has been estimated that an ounce of dog waste can contain 650 million fecal coliform bacteria. The EPA has estimated that two to three days’ worth of dog poop from a neighborhood with about a hundred dogs would contribute enough bacteria to temporarily close a bay, and all watersheds within 20 miles of it, to swimming and shellfishing.

In 1976, the Westport River Defense Fund was created in opposition to a septage lagoon proposed by the Board of Health that would have been built near the East Branch of this tidal river. The idea to construct a sewage pit by the river to dispose of the town’s septage pump-outs created a major controversy, and resulted in what is now the WRWA.

“It didn’t happen,” Carvalho said. “It was our first victory.”

Since that battle nearly four decades ago, the Alliance has grown from 15 members to more than 2,000. Numerous projects have been developed over the years that promote education and advocacy — all in an effort to protect one of the region’s most significant coastal assets in both habitat quality and scenic beauty.

But the fact that 23 percent of shellfish beds in the Westport River are permanently closed for harvesting documents the continued problem of contamination, according to Carvalho.

In all, some 50 percent of the river’s total shellfish beds are seasonally or conditionally closed, and 76 percent of the river’s harvest potential is limited because of bacterial pollution, according to the WRWA..

“The river has gotten much better in the past 10 years, but nitrogen pollution, runoff and septic systems are still a concern,” said Carvalho, who has been with the organization for 13 years. “It’s a costly endeavor, but it is vital we protect our water resources.”

Nutrient loading and pathogen contamination are water-quality concerns, particularly in the upper reaches of the river’s 35-mile shoreline. The river suffers from the problem of eutrophication, especially in the upper East Branch. Carvalho also is concerned about the emerging threat of chemicals from personal-care products and pharmaceuticals. In addition, she believes Massachusetts needs to do a better job phasing out antiquated cesspools and replacing them with modern septic systems or municipal sewer. Westport, for one, doesn’t have public sewer.

WRWA staffers work with local schools to educate students, from kindergarten through high school, about the importance of protecting the watershed, and the organization has partnered with municipal and state agencies to run water-quality programs. The nonprofit also promotes the use of buffer strips, rain gardens and low-impact development technologies to help keep the river and its watershed clean.

WRWA has maintained a summer bacteria-monitoring program for the Westport River since 1991, and the organization’s collection and analysis of site samples has been used by municipal and state agencies to document bacterial contamination.

The Westport River watershed spans two states, Massachusetts and Rhode Island.The watershed

The Westport River has two branches. The smaller West Branch is about 7 miles long, rising from a confluence of brooks near the village of Adamsville, R.I. The West Branch separates the village of Acoaxet from the rest of Westport — one needs to pass through Rhode Island to reach the rest of the town.

The larger East Branch is about 11.5 miles long, rising at the border of Westport and Dartmouth, at Lake Noquochoke. After a short length, the river meets Bread and Cheese Brook before reaching the head of Westport village, where the WRWA will soon move into its new home. From there, the river continues southward, fed by several brooks, before an initial widening to between 100 and 400 yards at Widows Point.

Once in Westport Harbor, the combined branches bend around Horseneck Point, before flowing into Rhode Island Sound, just west of Horseneck Beach State Reservation, at the point where Rhode Island Sound meets Buzzards Bay.

The Westport River watershed encompasses parts of Westport, Dartmouth, Fall River and Freetown, and Tiverton and Little Compton in R.I., and 85 percent of the watershed’s landmass drains into the river’s two branches.

Frank Carini is editor of ecoRI News, where this piece originated.