The fact that the Charles River is clean enough to swim in almost goes against instinct. The constant reiteration of The Standells’ classic song “Dirty Water,” unofficially adopted by locals as something of the city’s war cry, has hammered home the notion that the Charles was and still is unfit for aquatic activity. But one organization is trying to keep Boston lore from coming in between residents and their river.

In September 2014, the Environmental Protection Agency (EPA) gave the Charles River a cleanliness grade of A- which marks the cleanest the river has been since it started receiving EPA grades in 1995. The Charles River Conservancy (CRC), stewards of the river and its surrounding landscape, has endeavored to remove the stigma of filth and contamination by promoting annual community swims.

“The Charles River is now the cleanest urban river in America,” said CRC project Manager Theresa Doherty. “We must meet very specific water quality standards set up by the Department of Public Health in order to receive an events permit for a swim from the Department of Conservation and Recreation, who operates the Charles and the parks around it.”

The implementation of swimming restrictions for the Charles River isn’t an isolated case and its not based solely on its historic impurity. For all Commonwealth waters operated by DCR, recreational permits are required as a matter of public safety – not all of them are overseen by lifeguards.But the Charles also has bacterial standards it must meet, courtesy of the Department of Public Health, including the amount of fallen precipitation 48 hours before a permitted event. If enough water accrues, it can wash over roads and parkways and empty into the river carrying along with it any debris and chemicals that could catalyze the growth of bacteria such as E. coli.

“Large amounts of rain also put a strain on the Combined Sewer Overflow system,” said Doherty. “While nowadays it is rare that the CSO system gets overwhelmed and triggers an outflow of sewage and rainwater (which are processed through the same sewers) into the Charles, it can occasionally still happen, temporarily increasing the e.coli count within the river.”

The Charles River is now the cleanest urban river in America

But the CRC is gaining momentum in its efforts to promote the swimmability of the Charles. Since 2013 the CRC has hosted community swim times that are only growing in popularity.

In 2013, for the inaugural community sessions, the CRC had 144 swum with 100 more people added to a wait list. In 2014, more than 200 people hit the water.

In 2015, the CRC is striving to double the amount of swimmers with additional park programming that includes events and expanded swim hours.

And, according to the CRC’s recent annual report of 2014, the CRC hopes to explore the best way to create a permanent swimming area for residents and visitors to enjoy on an extended basis.

“The Swimmable Charles Initiative is a major tenet of the Conservancy’s mission, so we talk about our swim events at all of our CRC events and do our best to advertise the swims (and get as many new swimmers as possible!) each year,” said Doherty. “That said, we have a good number of Bostonians to win over, and I look forward to talking to many more people about the increased recreational potential of a clean Charles River.”