Even in cold January, when the woods are stripped bare, it’s clear why so many Maryland environmentalists compare the Mattawoman Creek to Eden. Eagles alight from barren trees and glide over serene waters, flocks of ducks darken the winter sky, and fish leap in the muddy shallows.

Yellow perch will soon make their annual run to spawn by the tens of thousands in the Mattawoman, a feast for raptors. They release milky strands with 60,000 eggs each, bolstering the Charles County creek’s status as “the most productive tributary to the Chesapeake Bay,” according to state fishery biologists.

And for years, the county planned to build a highway right through the watershed.

But recently a strange thing happened. Local environmental activists actually won a fight against a development that they said would harm wildlife. The state said no to the road in a rare denial of a development permit after the activists relentlessly picked apart the county’s arguments for it in an application.

The demise of the half-built $70 million Cross County Connector is being held up as a victory over urban sprawl that could be duplicated throughout the fragile Chesapeake Bay watershed.

“There’s great enthusiasm for using the Mattawoman as a poster child for how the bay can be saved,” said Bonnie Bick, vice president of the Mattawoman Watershed Society.

Early in the fight over the connector, opponents were a huge long shot to win. Like a boxer who takes a multitude of jabs to land one solid punch, they acknowledged suffering a series of defeats in failed efforts to get county planners to propose development designs that were friendly to the creek.

The proposed 16-mile connector was designed to start at Route 5 and cut through small winding roads and the Mattawoman and end at Indian Head Highway. Eleven subdivisions with more than 2,000 homes were proposed, and were seen as likely to lead to more storm-water runoff laced with sediment and nutrient ­pollution — and foul the Chesapeake.

Mattawoman Creek is like many of the bay’s tributaries. It’s good looks are only skin deep. Below its emerald tree canopies in Mason Springs are waters with shrinking populations of yellow perch, white perch, herring and largemouth bass.

Walking through the area last week, Mason Springs Conservancy board member Ken Hastings explained how storm-water runoff from development, floods and sewage overflows have eroded and reshaped its banks, widening them, slowing the current, making the area less attractive for fish.

Yellow perch disappeared from a part of the creek near Route 225 in the 2009 spawning season, and the percentage of herring eggs found in stream samples dropped dramatically between 1991 and 2010, state fisheries biologist Jim Uphoff wrote in an unpublished analysis.

Still, the creek is considered to be the cleanest and most abundant tributary to the Potomac River, and one of the most valuable waterways on the Eastern Seaboard.

When the fourth section of the connector was completed near the watershed in 2010, the county applied for a state non-tidal wetlands permit to go through the Mattawoman — ripping out six acres of wetlands around the creek — and finish the job.

Backs against a wall and facing defeat, activists in groups such as the Mattawoman Watershed Society, the Chesapeake Bay Foundation and the southern Maryland chapter of the Sierra Club made a desperate lunge.

“That’s when a line was drawn in the sand,” Hastings said. “We went after the permit.”

The groups filed public information requests during the permit process to get the county to answer questions about the impact the road would have on the creek.

“Every time the county made a response about how they would lessen the impact, we the activists picked it apart, found it lacking, and reported our findings” to the Maryland Department of the Environment.

As a result, the state asked the county for more details, which required the county to spend tens of thousands of dollars on consultants to conduct engineering surveys and return with answers.

Late in 2010, four newly elected county commissioners entered office with concerns about the growing cost of applying for a permit, the road’s impact on the watershed and the $31 million it would cost to complete the road if they prevailed.

“No one on this board wanted to spend more money condemning land for this road,” said Candice Quinn Kelly, the board’s president.

“They had spent $35 million,” then dropped the ball on studying its feasibility, Kelly said of the county and her predecessors on the commission. Money needed to answer the state’s questions dried up.

In a November letter, state environment officials announced the inevitable. The application for a non-tidal wetlands and waterways permit was denied because the county failed to address basic concerns.

“The decision to abandon [the connector] because of extremely well-organized and opinionated environmentalists is a crime against Charles County,” said Jim Whitehead, a board member on the county chamber of commerce.

“This is an astronomically important road,” Whitehead said. “I don’t think [Mattawoman Creek] would have been harmed in any measurable way after the road was built. Nature is so powerful compared to humanity. It recovers remarkably well by itself.”

Reports by the Maryland Department of Natural Resources indicate the opposite. Twenty years ago, when the Cross County Connector was on the drawing table, the Mattawoman was a picture of health.

Between 1971 and 1991, researchers saw little change in the fish that swam from saltwater to freshwater to spawn. But four years ago, the fishery went into a troubling decline.

In addition to decreases in perch and herring spawning, the state fishery service has expressed concern over a possible decline in the creek’s lucrative largemouth bass fishery as the county’s development increases. Anglers spent an estimated $568 million in Maryland, mostly for black bass, according to the report, which cited a 2008 U.S. Fish and Wildlife study.

“In Charles County, fishing, boating and water-related activities generated more than $40 million per year and were the largest visitor and local resident activity under tourism,” Uphoff’s report said. The county Office of Tourism estimated that largemouth bass tournament fishing pulled in $7 million in 2010.

On a rainy Wednesday, John Page Williams of the Chesapeake Bay Foundation started the engine on his skiff and motored downstream on the Mattawoman to demonstrate how it is important to more than just anglers and tourists.

Williams pointed a finger high toward a barren tree. “There’s one,” he said, his eyes on a bald eagle searching for prey fish. Within 10 minutes, the boat passed another three bald eagles.

Over two hours, talking almost nonstop, Williams pointed out thousands of black ducks, mallards, great blue herons, white swans and geese, all dining on the creek in winter.

“There’s no bad time to be out here,” he said.