After six years of heated debate, the Charles County Board of Commissioners voted to restrict development in one of Maryland’s fastest-growing counties to protect one of the state’s healthiest — and most threatened — water bodies, Mattawoman Creek.

By a vote of 3–2, the commissioners approved a Watershed Conservation District, which will reduce potential development in the Mattawoman drainage basin and the headwaters of the Port Tobacco River. The vote follows an intense, nearly yearlong debate after the county adopted a new comprehensive growth plan that called for protecting the creek, a Potomac River tributary just 20 miles from Washington, D.C.

The conservation district limits builders to one house per 20 acres, half the density previously permitted under the county’s most protective zoning. More importantly, commissioner Ken Robinson said, it preserves land that developers wanted to build on; the real estate industry had estimated 17,000 additional homes could go in the Mattawoman watershed if the zoning had allowed the higher density that they sought.

“We honestly couldn’t have handled that,” Robinson said. “The fast growth of this county has put all of our natural resources on the brink. We had the opportunity to do the right thing here to protect them, and we did.”

The fight for the Mattawoman dates back at least six years, when an interagency task force that included the U.S. Fish and Wildlife Service, the state Department of Natural Resources, the Maryland State Highway Administration and the U.S. Environmental Protection Agency issued a report warning that the 30-mile long creek was in jeopardy from development.

Long known as a productive fish nursery and haven for biodiversity, it is ranked eighth out of 137 streams for freshwater biodiversity in Maryland and is home to six threatened or endangered species. In its 2011 report, the task force wrote that the estuarine portions of the creek “can be described as what a restored Chesapeake Bay would look like.”

That the Mattawoman could sit amid subdivisions and near highways and still retain its fragrant pawpaws and blooming lotus blossoms, its orblike yellow perch eggs and its vast forest cover, seemed an act of defiance. But not for long; DNR biologist Jim Uphoff, in a report comparing the Mattawoman with the more developed Piscataway Creek nearby, concluded that waterways reach a tipping point when more than 10 percent of their watershed gets covered by pavement and buildings. Piscataway had crossed the threshold; Mattawoman was on the precipice.

The zoning protection just adopted keeps impervious surface in Mattawoman’s watershed at about 8 percent, Robinson said. The commissioners were mindful of that tipping point.

Bonnie Bick, one of the founders of the Mattawoman Watershed Society, said members were “very thankful” for the vote. The grass-roots group got help in their fight for the creek from the Chesapeake Bay Foundation and the anti-sprawl group 1,000 Friends of Maryland.

Some of the opponents were talking about a referendum to oppose the plan, but Robinson said it’s unlikely. Most who opposed the plan were developers and outside groups, he said; property owners who wished to pass their land down to heirs that might want to subdivide it in the future had been permitted to do so through a provision in the plan. Only about 200 property owners were affected by the zoning changes.

The watershed plan is yet another move in the seesaw that is Charles County planning, which is under pressure from environmentalists to preserve, developers to build and residents to keep things the same lest they have to accommodate more portable classrooms and endure more traffic. Another commissioner election looms next year, but Robinson doesn’t expect this plan to change.

Bick said her group’s one disappointment is an exception in the plan that will allow development at Maryland Airport, a general aviation field that’s mostly forested. The group plans to continue fighting that.