Bacalar Lagoon boat tour

Pontoon boats leave from the docks along the shore in town for a two-hour run down the lagoon, a 50-odd kilometre strip of fresh water whose blues change with the depth over a white limestone floor. The stops are the deep Cenote Negro and Cenote Esmeralda inside the lagoon, the Isla de los Pájaros with its herons and parrots, and the Canal de los Piratas, a shallow channel smugglers once used, where you get in and float.

The banks of the canal are lined with stromatolites, rock-like colonies thousands of years old that break easily: do not stand on them or rub the clay on your skin, and go without sunscreen or with very little. The water is calmest in the morning, and the afternoon sailings dodge the worst sun. If a motorboat feels wrong here, the same lagoon can be done by kayak, paddleboard or sailboat.