Areas of the Nashua River are one step closer to possible protection as a bill sponsored by U.S. Rep. Niki Tsongas makes its way through Congress.

The bill, which passed through the House of Representatives last month, would authorize a study to see if parts of the river and its two tributaries, Squannacook and Nissitissit, could be enlisted in the National Wild and Scenic Rivers System.

Rivers that are officially part of the system are protected under the National Wild and Scenic Rivers Act, which seeks to preserve designated rivers in their free-flowing condition.

The river, which runs from Nashua, New Hampshire, through towns including Harvard, Ayer, Shirley and Groton, has come a long way from its polluted past. Waste from various mills and factories changed the color of the water and even caused an odor.

Cleanup efforts began in the 1960s with the initiative of Groton resident Marion Stoddart and the creation of the Nashua River Watershed Association in 1969.

The study authorized in the bill would examine about 16 miles of the river's main stem -- from Lancaster to the New Hampshire state line -- to see if it would be eligible for designation as a Wild and Scenic River.

It would also review 10 miles of the Squannacook River in the Ayer-Shirley-Townsend region and the Nissitissit River in Pepperell.

Normally, such studies run for about three years at $300,000, said Jamie Fosburgh, New England team leader for Wild and Scenic Rivers for the National Park Service. The money would come from the National Park Study, which would help form a study committee with the NRWA.

"That's an in-depth look at both the science of things but also very much the local community context of what can be done, what should be done," he said.

A 2013 NPS reconnaissance survey found that segments of the river have "noteworthy natural, cultural and recreational resource values" that met criteria to qualify as a river in the Wild and Scenic River system.

Elizabeth Ainsley Campbell, executive director of the NRWA, said the study process would take tremendous community involvement.

The study committee members would include representatives from each of the towns that the river segments flow through and any other relevant local stakeholders, she said.

"Together, the study committee members will figure out what they need to look into more in presenting a case to their communities -- and then potentially to Congress -- as to why it should be part of the Wild and Scenic River system," she said.

Part of the point in bringing stakeholders together, she said, is to find ways to reach out to citizens who are interested or who can lend a hand with a certain area of expertise.

"I think the study committee is sort of like the hub of a wheel, where the spokes will go out and not only touch a lot of other members but bring in advice to the committee from a lot of different people and sources," she said.

Designation as a Wild and Scenic River would qualify the Nashua River for annual federal funds, she said, in addition to adding federal protection.

The study would also determine a good management system plan for the river.

Presumably, the committee would find that it would like to go forward with designation, Campbell said. Then, it's up to the affected towns to express their will.