Bostonians may “love that dirty water,” but the Charles River may be running a little clearer by 2013.

The river will see a drastic decrease in contamination—specifically, “over a 99 percent reduction in combined sewage overflow,” the executive director of the Massachusetts Water Resources Authority (MWRA), Frederick A. Laskey, said yesterday.

Combined sewage overflow (CSO) refers to the contamination that enters the river through pipes containing both storm water and sewage spillover.

The move, slated for completion by 2013, could “perhaps make the Charles River the cleanest river in the country,” Laskey said.

This current cleanup effort is the result of a 1985 lawsuit for violation of the Clean Water Act of 1972, according to Ria Convery, the communications director for the MWRA. The MWRA was specifically created to undertake the court-order cleanup effort, Convery said.

The goal is to raise the water quality so that swimming is possible throughout the year, said Michael D. Wagner, assistant enforcement consul for the Environmental Protection Agency of New England, yesterday.

“The river is in good shape in dry weather,” Laskey said. “The problem is after or during rainstorms.”

Wagner added that the MWRA plans to reduce the CSO from 17.1 billion gallons a year in 1988 to 7.8 million gallons a year by 2013.

Laskey said that this move marks a “great day for the river and the people who use it.”

But Gordon McKay Professor of Environmental Engineering Peter P. Rogers said that the cleanup was long overdue.

“Rivers and lakes were supposed to be swimmable by 1983,” Rogers said yesterday. Because the “city of Boston did nothing to help this,” to say that “Boston is ahead of everyone else is a laugh,” he said.

The MWRA has appropriated $850 million for the cleanup of the CSO, according to Convery. But because the MWRA doesn’t receive any federal or state funding for the cleanup, this effort has proven to be difficult, she said. Convery said that she hopes the MWRA will soon receive state funding.