The porous limestone of Quintana Roo is saturated with distinct layers of freshwater and saltwater. The saltwater layer is deeper inland, due to the pressure of overlying freshwater. Groundwater flows are complex, with freshwater and saltwater flows toward the sea, and a small reverse inland flow deeper in the saltwater. Any contaminants in the freshwater layer will generally flow towards the sea, but contaminants in the saltwater layer may flow inland. Most cave formation is thought to take place close to the halocline because the water is chemically most active there.

Graphic is based on research by Patricia Beddows