From the greener suburbs of Montgomery County to urbanized Manayunk, the Wissahickon Creek courses through some of the region's most-scenic areas and alongside a well-traveled trail. It is a popular fishing, and even a swimming, stream.

It is also a troubled stream; a source of concern, particularly since it supplies 10 percent of Philadelphia's drinking water.

The Environmental Protection Agency has identified the Wissahickon's water quality as "impaired," and efforts to improve it have been more than a decade in the making.

But under a new EPA initiative, efforts to clean up the Wissahickon stand to get a significant boost this summer.

One long-standing impediment to improving the water quality has been that 16 different municipalities - with 16 different governments - are part of the Wissahickon watershed.

"The EPA has put in some very strict standards as far as water-quality levels," said Laurie Grant, director of institutional advancement at the Wissahickon Valley Watershed Association, "and one that the municipalities sort of balked at."

Under a proposed intergovernmental agreement, they would not be on their own. The 16 towns would share the cost of the planning process - a key step in the cleanup - with the help of a $1 million grant from the William Penn Foundation.

Collaboration among the towns is crucial, since it is impractical for one municipality to meet EPA standards if the creek is being fouled upstream.

The intergovernmental-agreement concept, now being used across the country, represents an alternative to the traditional EPA regulatory system.

"It is fairly new as a vision for the agency," EPA spokesman David Sternberg wrote in an email. For towns in a watershed, he said, "The idea is that they could achieve water-quality standards in a more efficient, less costly way."

The EPA regulations call for reducing phosphorus in the Wissahickon. An EPA report said the sources are wastewater-treatment plants and municipal storm-water sewers.

Planting trees and gardens to trap and filter rainwater can reduce the phosphorus level, said Patrick Starr, executive vice president of the Pennsylvania Environmental Council. That, of course, would require intergovernmental cooperation.

"You can enhance the water quality, and you can improve the community with attractive rain gardens with flowers in them," Starr said. "And riparian buffers that make the creek more attractive for human recreation."

Eleven towns in Montgomery County still are reviewing the agreement. If they all sign on, the plan would proceed.

Five municipalities already approved the agreement and committed financial contributions to the planning process, which will look at ways to improve the water, reduce flooding and erosion, and protect fish.

Ambler's borough council reviewed and discussed the plan this week, and will vote next month.

Borough Manager Mary Aversa said the plan could be a good option for Ambler because the borough is so built-up that it has acute storm-water-management issues.

"It's an urban small town, and when the majority of this town was built there were not storm-water requirements," she said.

If Ambler had tried to act on its own, she said, "everything you do is in vain," as pollutants travel from communities upstream into the waters for which Ambler is accountable.

The plan still is subject to approval from all the local governments, and federal and state regulators would review the final proposal from the planning process, expected to take two years.

But those involved are optimistic.

"Everybody's got a voice at the table, and everybody has a stake in it," Grant said of the watershed association. "It's really a rare opportunity."