Sian Ka’an The Sian Ka’an Biosphere Reserve (85mi south from Cancun) is the habitat of an extensive fauna: more that 325 species of fowls and 101 different mammals have been classified. Inside its lagoons, which are maintained with underground rivers and surrounded by mangroves, it’s common to see manatees, along the 74 mi of beach. White and Howksbill turtles arrive during May and December to lay their eggs. The coral reefs are part of the Great Mesoamerican Reef, the second largest reef on the planet. The group Amigos de Sian Ka’an, has office in Cancun, it offers several departure times with previous booking.