This map shows the hydrologic regions that make up a great part of the Estuario de la Bahía de San Juan basin, which is 97 square miles (251 km2) (Comprehensive Conservation and Management Plan, 2000).

These regions were determined by the Office of Water Plan of the Department of Natural and Environmental Resources of Puerto Rico.

From left to right you can see the coastal area of Ciénaga Las Cucharillas, followed by the Río Piedras basin in the center, and the coastal area east of the Estuario de la Bahía de San Juan on the right.

As you can see, the boundaries of the Estuario de la Bahía de San Juan basin has rivers and ravines that pass from the high zone, as well as canals, lagoons, and beaches in the coastal zone where freshwater and saltwater combine.

A hydrographic basin includes the surface area of ​​a zone or region where the topography generally controls runoff to a single point (Puerto Rico Water Resources Inventory, 2004). The coastal areas of indefinite drainage to the sea (Quiñones and Torres, 2005).

This region has three sub-basins which are also designated hydrological regions: the Estuario de la Bahía de San Juan, the Río Piedras basin, the Ciénaga de las Cucharillas, and a small fragment of the Río Grande de Loíza, among other smaller regions.