Bacalar Lagoon holds no rivers, no tributaries, and no outlet to the sea — its seven distinct bands of turquoise and cobalt are fed entirely by cenotes threading upward through limestone bedrock. The Spanish called it Laguna de Siete Colores in the sixteenth century, though the Maya had already named the settlement Sian Ka'an Bakhalal, "place where the sky is born," centuries earlier. The water column stratifies by temperature and mineral density, each thermocline refracting light at a different wavelength. The result is a gradient so sharp that sailors report crossing from pale jade to midnight blue within the span of a paddle stroke. Pontoon tours became the lagoon's signature access model in the early 2010s, replacing narrower motorboats that churned sediment and fragmented the stromatolite colonies lining the western shorebank. These microbialites — layered structures built by cyanobacteria over three thousand years — form living reefs that rank among the oldest biological formations in Mesoamerica. Bacalar pontoon boat tour operators now follow marked channels that skirt the stromatolite zones, pausing at designated swim stops where the lakebed drops to fifteen meters and visibility extends past twenty. The lagoon's southern basin, known as the Cenote Negro, plunges to ninety meters, its walls draped in submerged tree roots that divers describe as inverted cathedrals. Group sailboats and motorized pontoons share the same departure docks along Avenida Costera, each vessel configured for eight to twenty passengers. Most bacalar lagoon boat tours include a stop at Cenote Esmeralda, a shallow depression where the water temperature climbs four degrees above the ambient mean, and at Cenote Cocalitos, where swimmers float above stromatolite domes visible two meters below the surface. Open bar service — typically rum, beer, and agua fresca — runs throughout the circuit, paired with seasonal fruit cut at embarkation. The lagoon operates under federal environmental protection status as of 2020, limiting daily vessel counts and mandating biodegradable sunscreen at all swim zones. Departure windows cluster between eight and ten in the morning, when the water lies flat and the light angle separates the color bands with maximum contrast. By midday the wind picks up from the east, flattening the gradient into a single milky blue.