It is located in the center of Tamaulipas and is made up of the basins: Laguna de San Andrés - Laguna de Morales, Río Soto la Marina, Río San Fernando, and Laguna Madre. It has a course of 416 km and covers 21,183 km2. Its nascent course is located in the east of the Sierra Madre Oriental, resulting from the confluence of the Purificación River and the Corona River. It then flows eastward, and after crossing the northern part of the Tamaulipas mountain range. When it arises again and continues its course, the river, with the name of Río Soto La Marina, flows thanks to the contribution of the Jiménez stream. Subsequently, its course heads south and then passes through the town of Soto la Marina, where it receives the contribution of the Las Palmas stream. The Soto La Marina river is the one that flows into the Gulf of Mexico, specifically in the Laguna Madre.