Anillo de Cenotes. 02/02/09; Yucatán; 891 ha; 20º43'21"N 089º19'23"W. A complex of 99 cenotes (or sinkholes) that cover approximately 5 km wide with a radius of 90 km in a zone of high permeability. Anillo de Cenotes ("ring of cenotes") is a unique water system in Mexico and the world and is the product of a large meteor impact 65 million years ago, the Chicxulub Crater, which fractured the surface layers of the Earth's crust and led to the ring alignment of the aquifer outcrops. It forms a cavernous complex network which acts as a weir and pipeline of large bodies of water. These cenotes serve as resting grounds for waterfowl during their migration to the South and hold endemic species of reptiles, such as the Yucatan Box Turtle (Terrapene carolina yucatana), amphibians like the Yucatan Mushroomtongue Salamander (Bolitoglossa yucatana), and birds such as the Ridgway's Rough-winged Swallow (Stelgidopteryx ridgwayi), the Yucatan Jay (Cyanocorax yucatanicus), and the Black Catbird (Melanoptila glabirostris). The cenotes are also home to a number of endangered or threatened species, such as the fish species Ogilbia pearsei, Ophisternon infernale, and Poecilia velifera. Among the factors adversely affecting the site are the accidental introduction of exotic species, environmental changes due to tourism, and the extraction of large volumes of water for tourist resorts. Ramsar Site no. 2043. Most recent RIS information: 2009.