It is a valuable 81482-hectare coastal strip that extends amongst the Municipalities of Celestún and Maxcanú in Yucatan, and Calkiní in Campeche, which was declared Biosphere Reserve on July the 19th of 1979 due to its flora and fauna richness, and for being part of the best preserved corridor of wetlands west of the Yucatan Peninsula.

The Celestún Estuary, a mainland valley invaded by sea waters, is rather shallow but with very high salinity levels. The artemia, a small crustaceous that constitutes the main diet of the pink flamingo (Phoenicopterus ruber), thus giving it the characteristic colour of its wings, reproduces on its muddy soil.

The flamingo is an aquatic and gregarious bird that nests and mates along the coast of the Yucatan Peninsula, from the Celestún Estuary, up to Holbox to the east. It is one of the most representative birds amongst the 333 species dwelling in the park, of which 117 are resident, 142 migratory and 14 of mixed habits.

Amongst the species residing in the area, the Antillean tern (Sterna antillarum), the beach seagull (Larus atricilla) and the sea swallow stand out. Their combined populations add up to roughly 10000 individuals.

Due to their colourfulness, gracefulness and attractiveness, birds are undoubtedly the greatest tourist enticement of the reserve; however, other activities such as kayaking and crocodile watching can also be enjoyed in Celestún. Though if you prefer something rather quieter, opt for a pleasant hike across the forest, amusing rides on mountain bikes, or unusual strolls to identify snails.

Besides, the Biosphere Reserve contains 54 mammal species, amongst them the spider monkey (Ateles goeffroyi) and the jaguar (Pantera onca), and 95 reptile species, with the American crocodile (Crocodylus acutus) and the boa (Boa constrictor) standing out. There are endemic fishes as well, such as the Typhliasina pearsei and the Ophisthernon infernale. In total, the estuary is the habitat of 554 animal species.

The annual presence of sea turtles such as the carey (Eretmochelys imbricata), the loggerhead (Caretta Caretta), and the green (Chelonia mydas), which arrive to the Mexican coast in order to lay their eggs in the sand, constitute an event of much interest for biologists and travellers alike; but they are not the only ones performing this act.

The horseshoe crab (Limulus polyphemus), a marine arthropod considered a living fossil, also reproduces on the coastal sands and in part of the estuary's inlet.

The wetlands of Celestún present 8 types of vegetation, being the diverse varieties of mangrove the most representative of the zone (they occupy between 70 and 80 percent of the area). Amongst them the black (Avicennia germinans), white (Laguncularia racemosa) and red (Rhizophora mangle) are abundant.

Regarding the altitudinal ranges, the estuary is located between 0 and 8 metres above sea level. It has a tropical sub-humid climate with an annual average temperature of 26 degrees Celsius, and average precipitations of 800 cubic millimetres. The dry season goes from March to May and the rains fall strong between September and October, months in which hurricanes usually hit the zone.

The reserve is administered by the National Commission of Protected Natural Areas (Conanp). It is located about 80 kilometres west of Mérida, following Highway 281.

There are two important settlements inside the reserve: Celestún and Isla Arena, whose economy is sustained on fishing and the extraction of salt on a small scale. The former has a medium port that allows reaching it by sea.