Sian Ka’an (‘where the sky begins’ in Maya) was founded in 1986 and a year later declared an UNESCO World Heritage Site. The original portion was 526,000 hectares to which 92,000 more were added from the Uaymil area in the south. The reserve encompasses most of the ecosystems that exist in the Yucatán Peninsula and is accordingly rich in wildlife.
There are medium and low-growth jungles, beaches, savannas, marshlands, mangroves and petenes or hummocks (patches of jungle around a cenote, on slightly higher ground in the middle of the wetlands); brackish and fresh water coastal lagoons, islets, cenotes, underground rivers, coastal dunes, sea grass beds, sand banks and 100 km of untouched and virtually unexplored coral reef.