Physicist Jim Long fell in love with the Mattawoman at first sight.

Who wouldn't? The Southern Maryland creek is like a chameleon. In the shallower parts, it looks like an enchanted forest-with a canopy of river birch and willow oaks. Ferns, flowers and shrubs, like the fragrant pawpaw, sprout from the ground. Where the sun peaks through, the water is clear enough to count the river herring.

The deep, open-water part is even more spectacular, covered in marshes thick with rice and lotus flowers unfurling their glorious blooms. Kayakers glide past in awe; anglers try their luck in the bass-rich waters. In its quiet splendor, the Mattawoman looks like it belongs in the remote areas of Costa Rica or Ecuador.

Instead, the Mattawoman is only 20 miles from the Washington Beltway, and therein lies its problem. It's in the fastest-growing region of the state. And it wends through some of the last undeveloped stretches of its corner of Charles County.

The county commissioners and other local politicians are pushing to build the Cross-County Connector, a road that would cross Mattawoman Creek and bring development to the Indian Head peninsula. They note that the road has been in the planning stages for nearly 30 years. They have cleared nearly every planning hurdle and are not asking for any state or federal money. Nearly two-thirds of the 16-mile road has already been built-only the contested stretch planned near the Mattawoman remains. Government officials believe they can mitigate the effects of the road and the impervious surface it will bring.

Long and his fellow volunteers at the Mattawoman Watershed Society argue that no mitigation will save the Mattawoman from the devastating consequences of more building. Several environmental groups, including the Chesapeake Bay Foundation, are working with them to stop the road. Also raising concerns about the Cross-County Connector are the Maryland Department of Natural Resources and the U.S. Fish and Wildlife Service.

Charles County commissioners contend that the road will not cause major impacts. But scientists and activists say development has already hardened 10 percent of the creek's watershed, and it can't take much more before the creek is seriously degraded. Already, the stream's populations of river herring and white perch are showing declines. According to estimates from the Department of Natural Resources, if the road is built, the Mattawoman will eventually reach 22 percent impervious surface. If that happens, and the creek follows the pattern seen in other waterways with developed watersheds, one of the Western Shore's most valued creeks will cease to be productive. Plants and fish will die.

"The creek is telling us just what the scientists have been telling us to look for," Long said as he stood knee-deep in the creek, counting fish eggs. "The Mattawoman is a poster child for the issue of land use impacts to the Chesapeake Bay."

The road's last hurdle is obtaining two permits, one from the Maryland Department of the Environment and the other from the U.S. Army Corps of Engineers. Those agencies would need to grant the county permits to disturb wetlands and specially protected waterways. Old Woman's Run, a Mattawoman stream, was designated as a Tier II waterway-a designation for a water body of excellent environmental quality. A decision from the two agencies is not expected until the end of the year, after Maryland's gubernatorial election.

Long has been counting eggs each spring for about 10 years. Not long ago, he would see hundreds of tiny orbs floating in his glass jar. This year, he saw about two each time he sampled.

Jeff Horan, DNR's director of watershed services, said the Mattawoman remains as close to ideal conditions for a stream as exists in Maryland-except for the fish. Counts are down for most species. It could be because of an excess of road salt used to treat winter's extreme snowfall. But it also is likely from the development that has already come.

State Sen. Thomas "Mac" Middleton, who served on the county commission from 1984 to 1994, said the county took a lot of care in developing a growth plan and in detailing a road that would mitigate negative impacts.

"We changed the course of the road. It's not like we have said we don't care. I do care, but I'm a realist. We're a beautiful county, we're 25 miles south of D.C., and people are going to continue to move there," he said. "I think it probably will have an impact on the Mattawoman, but if there are impacts, how do you mitigate it?"

It is hard to show the downsides of a road that doesn't yet exist. But DNR fisheries ecologist Jim Uphoff put out a report called "A Tale of two Creeks," which compares Mattawoman to Piscataway Creek in Prince George's County.

"In Piscataway, which has undergone the development that the Mattawoman is slated to have, the anhadromous fish spawning has, in fact, ceased," Uphoff said.

Also of concern are rare and endangered species in the Mattawoman watershed. The Maryland Department of the Environment is looking into the possibility that Krigia dandelion, a small, yellow flower, and Melica mutica, a two-flower watergrass, would be threatened by the construction.

The fight to stop the road is almost as old as the plans to build it. In the 1980s, when Charles County designated its growth area-which is larger than the entire District of Columbia-the area included the Mattawoman. The commissioners built a large sewage treatment plant in the watershed to handle the growth. Then they approved Chapman's Landing, a 4,600-home development on 2,100 acres in Chapman's Forest near the Mattawoman's headwaters. The project was zoned and had the necessary wetland permits.

But to then-governor and Smart Growth champion Parris N. Glendening, the project was little more than sprawl. After months of negotiations, Glendening had the state buy the land for $28 million. The commissioners and some of the governor's own advisers criticized the purchase, in large part because the development had already mitigated for environmental impacts and because the price was so high. But environmentalists cheered the decision.

Especially grateful was Bonnie Bick, a longtime Mattawoman activist. She believed the battle had been won, and the road would disappear shortly after the Chapman's project did. But it didn't. And developers began proposing even more development in the area.

Since 2005, Mattawoman has had a total maximum daily load, which is supposed to limit the pollution that can flow into the creek. So far, only a few rivers in the watershed have TMDLS, but the EPA is requiring them for all tributaries. Last fall, EPA officials began a series of hearings to explain the new requirements, and Bick made sure she and her fellow advocates argued their case to protect the Mattawoman at hearings in Baltimore and Annapolis, and at a Clean Water Conference in Washington where several congressmen and environmental officials, including Administrator Lisa Jackson, spoke.

"The Mattawoman could be a big win for the Chesapeake, at a time when all eyes are on the Bay," Bick said. "You have to wonder, what is the hope for the rest of it if the TMDL doesn't work here?"

Bick is indefatigable when it comes to advocating for the creek and for land preservation. She walks with a cane, the result of a broken pelvis and other injuries she suffered in a car accident in St. Mary's County in 2004. The crash occurred on her way back from a protest against then-Gov. Robert V. Ehrlich Jr.'s plan, later scrapped, to sell several hundred acres of a protected state forest to Baltimore developer Willard Hackerman. But her injuries don't appear to slow her down as she crisscrosses the state on behalf of her beloved creek.

Her efforts are gaining traction. She has met with J. Charles Fox, Jackson's point-man for Chesapeake Bay. Last year, American Rivers, a national nonprofit, put the Mattawoman on its list of the nation's most endangered waterways. The creek has been featured on draft maps of the Treasured Landscapes initiative, which is trying to protect large-scale landscapes in the Bay watershed.

The strength of her citizens' group spurred the Chesapeake Bay Foundation to get involved, which it rarely does in local land disputes. The last time the foundation officially entered one of these fights was in 2006, when farmers and environmentalists in Dorchester County opposed a project to bring several thousand homes and a hotel and conference center to a rural area near the Blackwater National Wildlife refuge. That fight ended with then-Gov. Ehrlich agreeing to buy the property just a few days before Election Day.

Later this year, Ehrlich will challenge Gov. Martin O'Malley, who beat him last time around, for the state's top job. Reminiscent of the 2006 election-year efforts, CBF and the Mattawoman Watershed Society are urging constituents to contact O'Malley in hopes of defeating the project.

"We know what we need to do to clean up the Mattawoman," said CBF advocacy manager Terry Cummings, "and yet, we are doing the opposite."

Environmentalists would rather focus the county's growth in Waldorf and keep it out of Mattawoman. They are pushing a rail line from Waldorf to the Branch Avenue Metro Station in Prince George's County. The county and the state have already endorsed the plan. But Middleton and others have been working on that since 1988, and the rail line doesn't seem imminent as funding is tight.

Opponents know it is hard-almost impossible-to kill a road project. Montgomery County activists fought the Inter-County Connector for nearly three decades. The first part of that road is slated to open later this year. More often, agencies get together to mitigate the impacts of the project. But DNR's Horan is not confident that can be done in the case of the Cross-County Connector.

"You cross a threshold, and really, limiting impacts may not be enough," he said. "I haven't given up on the Mattawoman yet. But, if the 22 percent (impervious surface) comes to pass, then we will have lost it."