Jacob Slaton for The New York Times

The barns of C&H Hog Farms can be seen among the trees. Many nearby residents wonder how such a large facility ended up in a major tourist area.

MOUNT JUDEA, Ark. — Anita Hudson's moment of realization came early this year when she saw cement trucks whizzing past her home in this blip of an Ozark town. For Sam Dye, it was when an employee at the school where he once was principal pointed out bulldozers clearing a wooded area in the distance.

For many months, Ms. Hudson and Mr. Dye had been among those who brushed off rumors that a large hog farm would be built here in the scenic watershed of the Buffalo River.

But now they were confronting reality: a farm that could house as many as 6,500 hogs was being built near them, within the pristine ecosystem of the Buffalo — designated America's first "national river" and overseen by the National Park Service. Since then, the operation, C&H Hog Farms — which began producing piglets for the agricultural giant Cargill in the spring — has divided the community, drawn scrutiny from environmentalists, politicians, and state and federal officials, and left many wondering how one of the largest hog operations in the so-called Natural State ended up in the heart of a major tourist area.

For environmentalists, the development of the Mount Judea (pronounced Judy) hog farm provides a stark example of what they see as lax oversight of such farms by state and federal regulators. Many of them were dismayed last year, for instance, when the Environmental Protection Agency withdrew proposed regulations that would have required all concentrated animal feeding operations, or CAFOs, to submit "basic operational information" and would have increased the number of such farms that require permits.

But C&H Hog Farms has many supporters, who say that these farms have long dotted the watershed without causing major environmental damage. They argue that the owners of C&H followed all the required steps to obtain a permit and will do all they can to make sure that the farm does not hurt the ecosystem.

"We believe that modern farming and environmental conservation and protecting the environment can coexist," said Mike Martin, a spokesman for Cargill. "A lot of the fear and concern is based on a 'what if' scenario that may never take place."

The controversy simmers as a report released in October by a group of Harvard-led scientists found that nitrogen levels were too high in about half of the country's national parks — in large part because of ammonia emitted into the air by agricultural operations, which can deprive fish of oxygen or drive out some vegetation in an ecosystem. This phenomenon is expected to worsen in coming decades as corporate farming increases, according to the report.

In response to the uproar here, the state has temporarily imposed more stringent notification requirements for future CAFO applicants, acknowledging that many crucial players, including the superintendent of the river and the director of the state agency that permitted the operation, knew nothing about the project until after it had been approved.

Gov. Mike Beebe of Arkansas, a Democrat, has allocated more than $340,000 to test and monitor the water quality in the watershed. Both of Arkansas' United States senators — John Boozman, a Republican, and Mark Pryor, a Democrat — have said they were concerned about the location of the farm, and supported close monitoring.

Environmental groups have filed a federal lawsuit against the Farm Service Agency and the Small Business Administration to try to block $3.4 million in loan guarantees for the farm, arguing that the agencies had not properly considered its environmental impact.

"I was just sick over it — I just couldn't believe it," said Jewell Fowler, 87, who found out about the hog farm after it had been approved, through a notice in a local newspaper. Born in Mount Judea, Ms. Fowler has lived for the past four decades in a wooden cabin on the banks of the Big Creek, one of the main tributaries to the Buffalo River: a quiet oasis where the trees emit a sugary scent and water laps over rocks in a soothing whir.

"I'm just afraid of the stink, maybe contamination, make people sick," Ms. Fowler said.

But the farm in Mount Judea has received considerable support, not least from some residents who live close by. Many see it as an economic bright spot in Newton County, which has high poverty.

On a recent chilly morning, a scent evoking a mucky lagoon curled over the hill where Glen Ricketts lives. He cracked a smile.

"You smell it," he said.

From Mr. Ricketts's property, looking down a valley in the distance, a pair of white triangular roofs pop up like fins amid a sea of trees. They are the large barns that house the pigs.