Sistema Ox Bel Ha is a cave system located underwater. It is, until now, continuously vying to be known as the longest underwater cave. This coastal cave is layered with freshwater that flow on top of the seawater, thus making it a halo cline, a mixing zone of water with unequal densities. The halocline at the Sistema Ox Bel Ha is measured at 25 to 52 feet deep, while the cave's total length is 231.17 km with a depth of 34.7 m. The cave can be entered through any of its 137 cenotes or pits. Located in Quintana Roo, Mexico, Sistema Ox Bel Ha was first explored in February 1996, and is considered ideal for advanced cave diving. The cave system is also frequented by tourists who go to swim and dive in the fresh waters surrounding Sistema Ox Bel Ha. It is also possible to exit into the Caribbean sea by swimming downstream the cave. The cave is surrounded by mangroves and many types of Savannah sea grasses. The isopods and the blind cavefish are some of the rare species of animals found in Sistema Ox Bel Ha. Summer may be the best time to visit Sistema Ox Bel Ha, because the climate is just right for exploring the different areas in the cave. Winter, on the other hand, may present conditions that make it difficult to traverse Sistema Ox Bel Ha.