Upper Reaches into Formosa Province: As the Pilcomayo enters Argentine territory, it transitions from a mountain river into a broad, meandering lowland system. The upper Formosa section is characterized by shifting channels, sandy and silty substrates, and dense riparian gallery forest. This stretch tends to carry higher sediment loads and can experience significant seasonal fluctuation in water levels.

Lower Pilcomayo and National Park Area: The lower section of the river, running through and adjacent to the Río Pilcomayo National Park, is the most ecologically rich and most visited by anglers. Here the river spreads into a complex wetland landscape that includes the main river channel, oxbow lagoons, flooded savannas, and interconnected estuaries. Laguna Blanca is the most prominent and well-known water body within this zone, offering calm, productive fishing waters surrounded by thick subtropical vegetation. The river in this section forms the natural border with Paraguay, and the park's remote character keeps fishing pressure relatively low.

Tributaries and Connected Waters: Several notable tributaries and connected water bodies enhance the fishing opportunities in the region, including the Dalmacia and Herradura channels, Colonia Aquino, Arroyo Ramírez, Villa Emilia, and the mouths of the Riacho Pilagá. These smaller waters often concentrate fish during seasonal flooding and drawdown cycles and are worth exploring as part of any extended fishing trip.