No one thought much about it when the largest lake in the Caribbean began rising in a year of heavy rains...Lake Enriquillo in the Dominican Republic has doubled in size over the past eight years, swallowing thousands of acres of farms and more than a dozen villages. In neighboring Haiti, smaller Lake Azuei has also steadily swelled, destroying homes and farms as well as disrupting trade by occasionally blocking a key cross-border highway. The two lakes are only three miles (five kilometers) apart and are fed by some of the same streams. It's been a slow-motion disaster and potentially catastrophic for two countries already burdened by major environmental challenges. The waters' rise has worsened exponentially in recent years, especially after heavy rains in 2007 and 2008 hit the island of Hispaniola, which both countries share. Tropical Storm Isaac dumped more water on the region last month, sparking more damage. While the cause remains a mystery, theories as to why the lakes are rising range from sediment and trash clogging the water system to increased rainfall from climate change and heavy storms. Dominican farmer Domingo Bautista recalls how the water gradually overtook his sugar cane, banana and sweet potato crop. Within two months, the family had to abandon their one-bedroom home in the sunbaked village of Boca de Cachon. "The water just crept up on us," said Bautista, who now works as a janitor at a roadside inn. "It didn't happen overnight."...In all, some 10,000 families have lost cattle, farmland or their homes. In Haiti, heavy rains made the situation worse last year and dozens of families were forced to evacuate. Many migrant laborers who cross into the Dominican Republic couldn't make the journey. "It's a clear environmental disaster," said Antonio Perera, the Haiti country manager for the United Nations Environment Program. "It's happening slowly, slowly, slowly, and you won't see the immediate effects like an earthquake or hurricane." Researchers have brought up several factors behind the rise of Enriquillo and Azuei, which both contain salt water because the low-lying region was once part of the ocean. Scientists have speculated that, on the Haiti side, massive deforestation has caused sediment to fill the lake while trash clogs the canals that would drain it. The lakes in both countries may also be growing because of heavier than average rainfall in recent years. On top of that, Perera said, Haiti's January 2010 earthquake may have shifted faults beneath both lakes and somehow altered the hydrology of the area, though water levels began rising years before the quake. "Two or three days after the earthquake there were springs everywhere in Thomazeau," he said, referring to a lakefront town on the northern end of Azuei he visited after the quake. "Even in the living rooms." Lake Azuei has expanded outward by about three feet per year for the past 10 years, growing to 52 square miles (134 square kilometers), according to satellite images captured in the City College of New York study. It was once only on the Haitian side but extends across the border by one to two kilometers, covering a Dominican customs office in brackish water. Similarly, Enriquillo's shores have moved out by about three feet per year over the past decade, reaching 128 square miles (331 kilometers), double the size of the lake in 2004. Many believe that the two lakes will soon merge as the water levels rise. Right now, they're separated by a road that often floods during heavy rainfall. Back-to-back storms in 2008 caused Azuei to spill and the border closed for several days, causing an untold loss in commerce. Like Enriquillo, Azuei is surrounded by cinderblock homes, and even a two-story resort, that are either partially underwater or completely so. Haitian farmer Cathleen Pierre and her family fled their home, now a part of Azuei, and live in a hodgepodge of shacks sandwiched between the lake and the mountains. The high cost of living in Port-au-Prince makes sure they stay there. "If the water rises again, we'll move farther up the hill," Pierre, 58, said as she hiked among her crops of corn and coconut. "We don't have another place to go." Despite the obvious concerns, both governments have done little to stem the rising water levels or help the families displaced by them. And it's not clear what the countries plan to do in the long term. Both sides are studying the phenomenon and have called upon the United Nations to implement a $2.5 million project that has planted thousands of fruit trees along the border. "The governments really need to get serious about this issue," said Jorge Gonzalez, a professor of mechanical engineering at City College of New York and the lead author of the July study. Authorities in the Dominican Republic have been sending food weekly to the poorest villages on the lake. They've also rebuilt broken water channels that were damaged in the 2007 and 2008 storm seasons. The Agriculture Ministry said it plans to relocate 500 families around the lake to give them fresh land for farming. The Haitian government, for its part, has laid gravel to elevate the road that leads to the southern border crossing, and Prime Minister Laurent Lamothe recently visited the area. The new environment minister, Jean-Vilmond Hilaire, said Haitian and Dominican officials were first trying to understand what was going on before coming up with a plan. "Both governments need to sit down and work to solve the problem," said Hilaire, who assumed the post in August. The rising waters have only added to the region's environmental challenges. Already, Haiti has only 2 percent of its forest cover left, after people deforested the mountains by chopping down trees to make charcoal. In the Dominican Republic, deforestation has hit more than 20 percent of the country. Plus, the lack of a proper sanitation system aggravated a deadly cholera epidemic that surfaced in Haiti the year of the earthquake and then spread, though mildly so, across the border. After 2007's Hurricane Noel caused the lake water to flood his home and crops, Bautista left his farm for the border town of Jimani. He spent three months there, waiting for the water to subside as he took odd jobs to get by. When he returned to Boca de Cachon, he found the water covered his house, which was stripped of its belongings by thieves. Bautista became frustrated while describing how little the government has helped him, and how he's forced to clean rooms at a love motel named El Encuentro, or The Encounter. "I have kids and I have to work because I'm not going to steal anything," Bautista said in the middle of a two-lane road where it vanished into lake water. "I have to earn a living for my family and will do it with my own sweat." --- Associated Press writer Evens Sanon contributed to this report from Port-au-Prince.