Chetumal Bay itself is the city's main natural feature — a vast shallow estuary fed by the Río Hondo that defines the border with Belize. It is also one of the few places in the world where you can still see the West Indian manatee, an endangered marine mammal that grazes the bay's seagrass meadows. A protected sanctuary covers the bay's eastern reaches, and sightings, while never guaranteed, are reasonably common from boats.
The water is too shallow and silty for great swimming in the city, but at Calderitas just north of town and further along the coast at Punta Estrella you can wade in from sandy beaches. Local cooperatives in Calderitas run boat trips to look for manatees and to visit the small offshore island of Cayo Tamalcab. The bay also supports an unusual mix of birdlife — ibises, herons, frigatebirds — that the manatee tours often double as.