Holocene stratigraphy on southern Ambergris Caye, Belize, records a sea-level rise over the last 6100 years, accompanied by major environmental changes and coastal reconfiguration that affected habitation at the Marco Gonzalez Maya site. At the time of initial occupation of the site at about 2100 B.P., sea level was about 30 cm below present stand, and the area was a relatively large, hospitable island surrounded by shallow lagoons open to the sea. Sea level reached present stand at about 1000 B.P., and by about 750--500 B.P. shoaling sedimentation and extensive colonization by mangroves had transformed the area into a dense swamp. Archaeological evidence suggests that population and construction decline, and virtual abandonment of the site by about the time of Spanish arrival in Belize about 1544 A.C., coincided with these adverse environmental changes. We suggest that sea-level rise and attendant environmental deterioration made the Marco Gonzalez site progressively more unsuitable for habitation, and forced the Maya to resettle to more favorable areas on Ambergris Caye.