LAGO ENRIQUILLO, Dominican Republic — Steadily, mysteriously, like in an especially slow science fiction movie, the largest lake in the Caribbean has been rising and rising, devouring tens of thousands of acres of farmland, ranches and whatever else stands in its way.

Lago Enriquillo swallowed Juan Malmolejos’s banana grove. It swamped Teodoro Peña’s yuccas and mango trees. In the low-lying city of Boca de Cachon, the lake so threatens to subsume the entire town that the government has sent the army to rebuild it from scratch on a dusty plain several miles away.

Jose Joaquin Diaz believes that the lake took the life of his brother, Victor. Victor committed suicide, he said, shortly after returning from a life abroad to see the family cattle farm, the one begun by his grandfather, underwater.

“He could not believe it was all gone, and the sadness was too much,” Mr. Diaz said, as a couple of men rowed a fishing boat over what had been a pasture.

Theories abound, but a conclusive answer remains elusive as to why the lake — as well as its nearby sibling in Haiti, Lac Azuei, which now spills over the border between the two on the island of Hispaniola — has risen so much. Researchers say the surge may have few if any precedents worldwide.

Bananas from outside of Lake Enriquillo. Jason Henry for The New York Times

“There are no records, to the best of our knowledge, of such sudden growth of lakes of similar size,” said Jorge E. Gonzalez, a City College of New York engineering professor who is helping to lead a consortium of scientists from the United States and the Dominican Republic studying the phenomenon.

Other lakes have grown, from melting glaciers and other factors, Mr. Gonzalez said, but “the growth rates of these two lakes in Hispaniola has no precedent.”

The lakes, salty vestiges of an ancient oceanic channel known for their crocodiles and iguanas, have always had high and low periods, but researchers believe they have never before gotten this large. The waters began rising a decade ago, and now Enriquillo has nearly doubled in size to about 135 square miles, Mr. Gonzalez said, roughly the size of Atlanta, though relatively light rains in the past year have slowed its expansion. Azuei has grown nearly 40 percent in that time, to about 52 square miles, according to the consortium.

The scientists, partly financed by the National Science Foundation, are focusing on changing climate patterns as the main culprit, with a noted rise in rainfall in the area attributed to warming in the Caribbean Sea.

In reports, they have noted a series of particularly heavy storms in 2007 and 2008 that swamped the lakes and the watersheds that feed them, though other possible contributing factors are also being studied, including whether new underground springs have emerged.

“People talk about climate change adaptation, well, this is what’s coming, if it’s coming,” said Yolanda Leon, a Dominican scientist working on the lake research.

The rise has taken a toll, particularly around Enriquillo, an area more populated than that around Azuei.

The government estimates that 40,000 acres of agricultural land have been lost, affecting several thousand families who have lost all or part of their only livelihood of yucca, banana and cattle farming. The town of Boca de Cachon at the lake’s edge is in particular peril, with some houses already lost, and the government is bulldozing acres of land for new farms.

A main highway to the Haitian border was flooded and had to be diverted, while another road around the perimeter of the lake now ends abruptly in the water.

Local residents are skeptical that the government will follow through, and they question whether the soil will be as good as the parcels near the lake that drew generations of farmers in the first place.

Olgo Fernandez, the director of the country’s hydraulic resources institute, waved off the criticism and said the government had carefully planned the new community and plots to ensure the area remains an agriculture hotbed. It will be completed this year, officials said, though on a recent afternoon there was much work left to be done.

“These will be lands that will produce as well as, if not better than, the lands they previously had,” Mr. Fernandez said.

A DRY ALTERNATIVE A government resettlement project for people affected by the rising waters. Jason Henry for The New York Times

Row upon row of cookie-cutter, three-bedroom, cinder-block houses — 537 in all — are being built in the new town, which will include a baseball field, church, schools, community center, parks, even a helicopter landing pad (“for visiting dignitaries,” an official explained). Environmental controls will make it “the greenest town in the Dominican Republic,” said Maj. Gen. Rafael Emilio de Luna, who is overseeing the work.

For now, though, at the ever-creeping edge of the lake, the ghostly trunks of dead palm trees mark submerged farms.

Junior Moral Medina, 27, who lives in Boca, plans to move to the new community. He looked out on a recent day on an area where his 10-acre farm had been, now a pool of lake water studded with dead palms.

“We have been worried the whole town would disappear,” said Mr. Medina, who now works on the construction site for the new town. “Some people at first did not want to leave this area, but the water kept rising and made everybody scared.”

Residents in other communities are growing impatient and worry they will not be compensated for their losses.

Enrique Diaz Mendez has run a small grocery stand in Jaragua since losing half of his six acres of yucca and plantain crops to Enriquillo. “We are down to almost nothing,” he said.

Jose Joaquin Diaz and his brother, Victor, grew up tending to the sheep, goats and cows of the family farm, but both left the Dominican Republic for the United States for better opportunity. Jose returned first, and three years ago Victor arrived, looking forward to the slower pace of life after working an array of jobs over 18 years in Brooklyn.

“We told him about the lake, but he was shocked when he saw it,” Jose recalled, tears welling with the memory.

Later that night, Victor called his mother to express his dismay. The next morning he was found hanging in a relative’s apartment in Santo Domingo where he was staying. “It is strange to see people fishing where we had the cows,” Mr. Diaz said. “Victor could not bear it.”