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The Charles River’s EPA grade just sank from an A-minus to a B

Sailboats on the Charles River in 2012.
Sailboats on the Charles River in 2012.(David L. Ryan/Globe Staff/File)

The Charles River’s EPA report card grade dipped from an A-minus to a B last year — but officials say while there’s still work to be done, it’s nothing to be overly concerned about.

The grade release comes as swimmers plan to jump into the Charles Saturday for the annual “City Splash” event, which seeks to celebrate “one of the cleanest urban rivers in the United States.”

The 2018 “B” grade, which was based on tests for bacteria in the water, means that the Charles met standards for “almost all boating and some swimming,” according to a statement from the Environmental Protection Agency Wednesday. The grade, which is based on samples taken during both dry and wet weather, sagged last year because of levels of bacteria during the wet weather period, which only met 47 percent of the state’s standards for swimming, and 91 percent for boating.

EPA officials noted that during wet weather conditions, higher bacterial concentrations and poorer water quality are more likely due to sewer overflows and polluted stormwater runoff.

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Still, the Charles is a lot cleaner than its “Dirty Water” reputation would have you think — the river’s grade has improved vastly since 1995, when it received a “D,” according to the EPA. Since then, sewer overflow discharges have been reduced, and enforcement of water quality standards and removal of illicit discharges have been increased, EPA officials said.

“For years, the Charles River has received consistently high grades for its water quality, enabling residents and visitors with an excellent opportunity to enjoy this incredible natural resource located in the heart of the Greater Boston area,” said Leo Roy, commissioner of the state Department of Conservation and Recreation, in the statement.

“It is clear from the data that the Charles, like Boston Harbor, has become a great recreational asset for all to enjoy,” said Fred Laskey, executive director of the Massachusetts Water Resources Authority. “We are pleased that the investments made by MWRA’s ratepayers continue to pay dividends.”

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However, some officials noted that there was still work to be done.

“The B grade is a reminder that while the Charles is much cleaner than it was when the first grade was given — a D in 1995 — our work is far from over,” said Emily Norton, executive director of the Charles River Watershed Association, noting that biggest challenges are mitigating stormwater runoff and extreme weather from climate change.

Emily Bender, a spokeswoman for the EPA, said she didn’t think there would be any concern about swimmers jumping into the water at the event this weekend.

“They really pay close attention to the water quality of the river, so no, they shouldn’t be concerned,” she said.