The Ría Celestún Biosphere Reserve protects 81,482 hectares of estuary, mangrove forest, and coastal dune where the Gulf of Mexico meets freshwater springs from the Yucatán aquifer. American flamingos congregate here in numbers that can reach 18,000 individuals during winter months, feeding on brine shrimp and algae in the shallow, hypersaline waters. The reserve was designated a UNESCO Biosphere Reserve in 1979 and expanded in 2000 to include critical nesting habitat on the barrier islands offshore. The flamingos are not permanent residents; they migrate between Celestún, Río Lagartos, and coastal lagoons in Campeche, following food sources and breeding cycles that shift with seasonal rains and salinity levels. Celestún village sits at the terminus of a 92-kilometer highway from Mérida, a route that crosses scrubland dotted with henequen plantations and limestone cenotes. The estuary itself is a drowned river valley, its mangrove channels flanked by red, black, and white mangrove species that stabilize the coastline and filter runoff from inland agriculture. Boat tours depart from the waterfront malecon, navigating narrow channels where frigatebirds and roseate spoonbills nest in the canopy above. The water transitions from brackish near the village to nearly seawater clarity at the mouth, where sandbars expose fossilized coral and mollusk shells. A Celestun flamingo tour from Merida typically includes transport along Highway 281, a boat excursion through the mangrove tunnels, and time at the beach near the lighthouse. The 54-peso conservation fee per person supports habitat monitoring and anti-poaching patrols coordinated by CONANP, Mexico's protected areas commission. Most departures leave Mérida between 07:00 and 08:00 to reach the reserve during the morning feeding window, when flamingos wade in shallow flats visible from the boat channels. The reserve is open 08:00 to 17:00 daily, though afternoon heat can push birds into deeper water or shade. The mangrove ecosystem here is one of the most productive in the Yucatán, cycling nutrients that support commercial fisheries for blue crab, snook, and corvina. Local cooperatives manage boat tours under permits that limit engine noise and approach distances to nesting colonies. The reserve's interior includes freshwater springs called ojos de agua, where cooler groundwater creates microclimates that attract migrant warblers and orioles during spring and fall passage. These springs are accessible only by guided boat, as the mangrove forest is too dense for foot traffic and the mud substrate too unstable for boardwalks.