The water quality at Dorchester beaches is improving, but is still bringing up the rear compared to other regional beaches, according to an environmental report card issued this week by a watchdog group. Save the Harbor/Save the Bay’s second annual Beaches Report Card is based of “thousands of samples” collected at 34 testing sites from Nahant to Nantasket by state authorities in 2012.

“2012 was a good year for most of the Boston Harbor region’s public beaches, with more than half earning either an A or an A plus,” said Bruce Berman, Director of Strategy, Communications and Programs at Save the Harbor/Save the Bay. "It was also a dry year, which explains most of the changes we saw from 2011. Bacterial pollution is often caused by storm water discharges that accompany summer showers, squalls and storms, so less rain means cleaner water."

Berman noted that Dorchester’s Tenean Beach once again was ranked lowest for water quality among the 15 beaches rated in the report. Tenean closed once every five days in 2012 because of high fecal bacterial levels, which can cause illness. However, the quality at Tenean was better than the year before— with a score of 81.82 percent in 2012, up from 79.50 percent in 2011. South Boston’s beaches once again topped the list of beaches tested daily, at 98.17 percent, followed by Pleasure Bay at 93.86 percent and Wollaston Beach in Quincy at 93.20 percent.

“At Save the Harbor/Save the Bay our goal is clean water and not simply better models or faster and more accurate test results. We are working towards the day when there is no need for flags at all,” said Berman.

"Just 25 years ago, these beaches were awash with human waste,'' Berman said. "We should be proud of what we've done and be prepared to finish the job."

John Sullivan, chief engineer of the Boston Water and Sewer Commission, said steady progress at Tenean Beach should follow an ongoing effort to ferret out illegal sewer connections that can drain into the ocean.
That tedious and difficult job should be done by next year, he said. He added that some waste can't be controlled, such as what is produced by birds, squirrels and other critters and carried by rainwater to the beach.

"There's no assurances ever that nature doesn't cause a violation,'' Sullivan said.

An Associated Press report contributed to this article.