HAMPERICO, Guatemala — In the waist-high estuaries that wind through the mangroves, bare-chested fishermen cast their nets only to haul them back empty. Crab traps with their plump bait lie untouched for hours. The desolate quiet is interrupted just by a few birds and the constant buzz of motorized pumps along the banks.

Those pumps, fishermen complain, have been their undoing in a town that is barely scraping by. The pumps belong to a shrimp farm and suck water from the mangroves to nurture 54 corporate ponds that need to be flushed every 10 days as they raise shrimp for export. Other pumps release gallons of foamy brown organic waste from the ponds, residents say, leaving a bubbly slick covering parts of the estuaries.

Farm-raised shrimp have become a cash crop in Central America thanks to an almost unending appetite for them in the United States, Europe and Japan. What was once a culinary treat has become as common as salt and pepper shakers on tables. Guatemala has relatively few farms, but neighboring Honduras has become a leading exporter.

Although the farm here, Camarones del Sur, is this town's biggest employer, it has since May also become the source of its biggest conflict, after two residents were killed by the police and the farm's guards in protests against the company.

Residents insist that the pumps and waste have depressed the water level, choked off oxygen and killed fish and that the security fences around the farm have blocked access to more bountiful waters.

"All the species in the mangroves are dying, and the water is at half its level," said Antonio Isolidarit Godoy Hernández, who has been fishing more than 13 of his 27 years. "There is no life in the mangroves. Now there are no baby fish. With no reproduction, what little is here is over."

At stake is the balance between the rights of companies that invest in the shrimp farms and the needs of traditional fishermen who have found it increasingly difficult to survive. Officials who have participated in government-mediated talks to resolve the conflict said it also showed how a developing country's need to lure jobs and investment was often accompanied by lax enforcement of environmental regulations.

"You can do what you want here," an official in the talks said. "Everyone pollutes here, and no one says anything."

Environmentalists and residents insisted that the farms, which started appearing in Latin America about 20 years ago and have grown with aid from the World Bank, have destroyed mangroves and led to pollution and conflict, not just here, but also in Mexico and Honduras. Worldwide, the farms produce 40 percent of the total volume in shrimp, according to the Food and Agriculture Organization, with many destined for the United States, Europe and Japan.

"These shrimp are produced for export, and the United States is a huge market where shrimp is the second most popular seafood after tuna," said Jacob Scherr, head of international programs at the Natural Resources Defense Council. "It is a huge multibillion-dollar business, and what you see in a sense is some of the poorest people in the world competing for the use of coastal resources with some of the richest consumers on the planet."

Executives of Camarones del Sur, or Camarsa, paint the opposite picture, saying they have followed industry trends and neither blocked access to the estuaries nor polluted them. Their ponds are on high ground, not carved out of the mangroves to take advantage of the shrimp's natural breeding environment.

Company executives also said their sponsorship of a 550-student school for the town, as well as medical checkups for residents, exemplified their desire to be a good neighbor. Like the protesters, they insisted that they had been victims of violence, even though the police have not arrested any protesters. Several guards were arrested, however, after they shot and killed one person in the recent confrontation.

About the sole point of agreement between the company and its opponents is that Champerico is desperately poor.

"We have not restricted access to the estuaries at all," said Domingo Moreira, an American who is president of Camarsa. "It is sort of a complex issue gravely exaggerated by economic problems in the whole country and the region."

The poverty is evident along the potholed streets, where groups of men on wobbly bicycles rush up to greet drivers and make rapid-fire pitches for beach-front restaurants. People looking for bargains root through the piles of used clothing and shoes that are stacked on pickup trucks or at curbside. Near a dock that is a rickety mess, fishermen return from hours of work with barely anything to show.

The town once thrived on its port, where coffee and cotton were loaded and shipped until the 1960's. When that dwindled, many people, including children, began to rely on fishing in the abundant waters and the latticework of estuaries.

Residents and environmentalists said pumping water from the estuaries to refresh the shrimp ponds had lowered natural levels and killed fish. They also said water discharged from the ponds was full of organic waste that has killed more fish.

Elmer López, Guatemala's Greenpeace representative who has studied shrimp farms in Mexico, Honduras and Ecuador, said the warm water and soaplike scum in some estuaries indicated that the foamy runoff from the ponds was at fault. "It is very polluted, almost like the color of coffee in places," Mr. López said.

The fences have added to the conflict, environmentalists and residents said, because in some places the fences come up to the banks of the estuaries, rather than 110 yards from the water's edge, a criterion that they said the law required. Until recently, stretches of the beach were fenced off and the remaining paths strewn with thorny branches, making it hazardous for barefoot fishermen to reach other waters.

"That shrimp farm has made martyrs of half of humanity," said Santos Pimental Ávila, 74, a wiry grandmother who treks more than an hour along the beach to go fishing in the hopes of putting food on the table and money in her pocket. "They put thorns on the beach where I walk. They put up fences. They don't allow us to go to the estuaries. The way they are, if we don't get some fish, we don't eat, because there is no work."

Mr. Moreira of the shrimp farm said the lack of fish was a natural phenomenon that had hit the Pacific Coast for three years. He said the town was polluting the water, dumping sewage in a canal that fed into an estuary. The farm, he said, cleaned its water before discharging it. The government recently found that the estuaries were contaminated, but did not pinpoint a cause.

"We welcome any objective party to test the water," Mr. Moreira said. "I am willing to tell you that if our water is not going back in clean, then I'll close the farm the next day."

He said the fences did not impede access to the water, but were to deter thieves, a constant problem for shrimp farms. But, he added, the site was exempt from the 110-yard rule, because the land was titled before 1957.

In May, residents gathered in the town plaza to rally against the farm. When the company sent its lawyer to meet them, the group wound up attacking him. Residents said he had provoked them by not responding to their complaints but resorting to legalisms. The police were called. One person was shot dead.

The federal government appointed a mediating commission to consider pulling back fences, restoring mangroves and building a fishing port and a road. But the talks faltered when, residents said, the company would not discuss the fences. Another protest was held in front of the company office, and another person was shot dead, that time by guards.

Since then, the town has been tense. Gonzalo Funes, the local representative of the human rights prosecutor, who had been involved in negotiations and was sympathetic to the residents' concerns, said armed men had gone to his house and tried unsuccessfully to enter.

"I think the company has been informal and irresponsible in the talks, with the implicit support of the government," Mr. Funes said. "It is a political and economic question. The farms are an economic power. Clearly, you risk your life when you touch these economic interests."

Mr. Moreira said some villagers were exaggerating the problems, manipulating neighbors and even paying protesters. "There are people who have an agenda of their own," he said. "One version is people want to acquire property in the area to build a port. There are others who complain they want to get fishing licenses, which are limited, and the way to do that is to promote violence."

Although many residents want to see the farm closed, others remain willing to negotiate.

"It would be practically impossible to remove the farm," said Camilo Jesús de León, who is active in the protests. "But if they want to use the land for ponds, they should drill wells and find their own source of water. The company says that means red ink for them. Yes, but what does it represent for us?"