Cenotes are sinkholes or potholes or sinkholes collapse completely or partially filled with a surface layer of fresh water and sometimes a lower layer of seawater if they communicate with the ocean by faults or other conduits. They are found mainly in North and Central America, especially in the Yucatan Peninsula in Mexico. They act as natural sinks that can reach several tens of meters deep. When cenote is found submerged in a lagoon or other body of water, it is called the Blue Hole. The cenote Zacatón, northeast Mexico, is the deepest known in the world. A robot scuba diver, the DepthX, has explored and mapped. It reached its bottom at 318 m depth in May 2007.