Banco Chinchorro is the largest coral structure in Mexico and the Caribbean. This false atoll, with 115 km in length, is part of the Mesoamerican Barrier Reef System. It is located just over 30km from the southern coast of Quintana Roo, between the towns of Mahuahual and Xcalak. The extensive coral barrier forms an oval lagoon, where small islands protrude through the surface, and where there is an abundance of mangroves and various species of birds. The most important keys are: Cayo Centro, Cayo Norte and Cayo Lobos. Many reptiles, including iguanas and the American crocodile, inhabit the keys. It is estimated that Banco Chinchorro has a population of between 400-500 individual crocodile. Declared a Biosphere Reserve in 1996, the various marine ecosystems here are a refuge for species that are commercially exploited, like the threatened queen conch (Strombus gigas) and Caribbean spiny lobster (Panulirus argus).