The U.S. Environmental Protection Agency gave the Charles River a B+ for water quality during 2015.

The grade indicates that the Charles was meeting state standards for bacterial water quality for boating 95 percent of the time and for swimming 69 percent of the time in 2015, according to a statement from the EPA.

That's the same grade as 2014, and slightly lower than the A- in 2013. When the EPA launched the Charles River Initiative in 1995, the river was graded as a D.

Curt Spalding, the EPA's regional administrator, says efforts to reduce pollution in the river have been very successful.

"At a national level, this is extraordinary what's been accomplished here," Spalding told WBUR's Newscast Unit. "The returning use of the Charles as a contact — what I mean by that people can contact the water and use it safely — this is looked at as one of the great accomplishments in this country."

Earlier this month, the Charles River Conservancy unveiled results of a study that looked into the feasibility of creating a permanent swimming dock on the river. The study recommended a location in North Point Park, provided further water testing was done.

Spalding says he could support a proposal for a public swimming area on the Charles as long as it has proper oversight.