WASHINGTON (AP) – Salt used to treat icy roads has polluted three major New England rivers over the past century, but better wastewater treatment is slowly cleaning up other chemicals in the water, according to a report released Tuesday.

The U.S. Geological Service reviewed water quality data for the Connecticut, Merrimack and Blackstone rivers for much of the last 100 years, and concluded that human lifestyles have had a dramatic effect on pollution levels – for better and for worse.

“Certainly, this study shows that our lifestyles have an effect on the area’s rivers,” said Keith Robinson, the study’s lead scientist. “Using what we have learned from this study will help water resource managers and private citizens to understand what the future of New England’s rivers might be.”

The study looked at levels of sulfate, phosphorus, nitrate, chloride and solid residues in the three rivers that run through five of the six New England states. The most notable trend linked the increased use of deicing salt to an increase in chloride in the water.

Chloride levels in the Merrimack River, for example, skyrocketed 760 percent over the past century, while it jumped 344 percent in the Connecticut and 186 percent in the Blackstone.

The survey found that the Blackstone River in central Massachusetts and Rhode Island – often called the birthplace of the American Industrial Revolution – had the highest levels of all five pollutants.

According to the study, increased use of fertilizer and emissions from power plants led to greater levels of nitrate in all three rivers.

But stricter controls over phosphorus in detergents and soaps along with better wastewater treatment have paid off as phosphate levels dropped in all three rivers, particularly since the early 1970s.

Sulfate levels also dropped in recent decades, due mainly to a decrease in sulfur-dioxide emissions as a result of federal emissions controls and the conversion from coal to natural gas for electric power.

The Connecticut River, the longest in New England, flows from northern New Hampshire and forms the border between that state and Vermont before cutting through Massachusetts and Connecticut.

The Merrimack flows south from New Hampshire through northeastern Massachusetts. The Blackstone rises near Worcester, Mass., and flows south through Rhode Island into Narragansett Bay.

AP-ES-07-23-03 0938EDT