sentences:  The Centla swamps occupy the delta of the Usumacinta and Grijalva rivers, which empty into the Gulf of Mexico and the Laguna de Términos through numerous distributaries.The ecoregion includes year-round wetlands, and freshwater swamp forests which are inundated during the summer rainy season.The Usumacinta mangroves lie in the brackish-water zone between the Centla swamps and the open water of the Laguna de Términos and the Gulf.