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 yucas 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.