Caño Tiburones is the largest wetland in Puerto Rico . It is located in the north coastal plain near Arecibo and covers and area of about 7,000 acres. Delimited by the Río Grande de Arecibo, and the Río Grande de Manatí , Caño Tiburones receives fresh water from the karst and salty water from the ocean.

Because of artificial drainage that took place between 1947-1998 for agricultural purposes, the water table of this wetland was lowered below sea level. This led to seawater intrusion crating zones of salty and saline waters within the wetland. Saltwater intrusion occurs through four locations along the north coast. Salinity across the wetland varies depending on the location of the intrusion zones, tides, and freshwater precipitation.

Caño Tiburones provides a natural laboratory for the geosciences. Understanding this unique ecosystem, its evolution and the interactions with the ocean, the karst and human activities are vital. Fresh water from the karst and salty water from the ocean interact in this transition region, creating a unique habitat for many species.

This natural wetland has been exposed to contamination by aqueous effluents produced from industrial activities, waste disposal sites, local or municipal sewage, and agricultural activities where pesticides and plaguicides are commonly used. The location of the Arecibo Regional Landfill and other illegal dumpouts nearby the Caño constitute the additional sources of pollution.

In October 21, 1998 , the Government of Puerto Rico designated 3,428 acres as a natural reserve for its conservation, preservation and restoration. The Caño Tiburones Natural Reserve consists of estuarine, palustrine and lacustrine wetlands with around 200 animal species and more than 100 flora species .