The Biosphere Reserve of Sian Kaan, "where the sky is born" in Mayan, was established in 1986 and is now a UNESCO World Heritage Site.
Sian Kaan faces the greatest challenge of conservation:

To find a way to integrate human activities without compromising other forms of life contained within its boundaries. The reserve is approximately 1.3 million acres in size and spans 120 kilometres from north to south - comprising almost one third of the Caribbean coast of Mexico.

Sian Kaan is home to 103 known mammal species, 336 known bird species and an important nesting site of two endangered sea turtle species.

It contains three large core zones where human activity is limited by permission to scientific research. Low-impact human activities and sustainable development occur in the area of the reserve known as the buffer zone. The human population is estimated at 2,000 inhabitants, the majority of which are located in the coastal regions, especially in the fishing villages of Punta Allen and Punta Herrero.

Approximately one percent of the land within the reserve is privately owned. The reserve is thought to have been inhabited in the pre-Classic and Classic periods as part of the chieftanships of Cohuah and Uaymil. There are twenty-three known archaeological sites inside the reserve. Discoveries of human remains, ceramic pieces, and other artefacts have been dated up to 2,300 years old. The northernmost section of Sian Kaan (where Casa Nalum is) contains what is thought to be an ancient trade route through lagoons and mangrove channels between the cities of Tulum and Muyil.