In the region of the plain chaqueña most of the rivers belong to the slopes of the rivers Paraguay and Paraná and they respond to a summery pluvial periodic régime. The most important rivers that travel the territory formoseño are the Paraguay, the Paraná and the Red one.

The river Paraguay is the tributary one more important of the Paraná. It possesses a longitude of 2.550 Km. Grosso is born in the plateau of Matto, Brazil, in the mountains do Parecis and the Tombador.

This river is characterized by the presence of the Pantanal, depression 770 Km long and 60.000 square Kilometers that it acts like a giant makes spongy that it retains the waters in the rainy seasons and it allows them to drain cover once his capacity of natural reservoir.

The Bermejo is born in Bolivia, it travels the provinces of it Salta and Jujuy and it constitutes the limit between the provinces of Chaco and Formosa. In the year 1870, the river changed course, at the moment it flows for the one denominated river Teuco. That old bed, denominated Bermejito, unites in Fork with the Teuco again. Starting from then, the Red inferior carries out the journey until the outlet in the river Paraguay. The basin of the Red one has a longitude of 1.450 Km. The Red river possesses great sedimentary load that carries problems until in the delta from Buenos Aires, but until the moment, in spite of being very meandroso maintains a central axis. doesn't scatter toward any address. In the times of great growing, it surpasses their ravines flooding several Km to their sides, but maintaining their main bed.

The river Pilcomayo is born in the Bolivian Andes, and it drains in the river Paraguay. has a normal course until the vicinities of Tucumancito, from there until the vicinity of Jump Palmar, the river remains dry, another nascent one with the denomination of Inferior Pilcomayo begins from this town, until its outlet in the river Paraguay. The river Pilcomayo is characterized to have great sedimentary load that the level of its channel increases causing a high uncertainty. For this reason retrotrayendo left toward the west about 20 Kilometers per year. Today it penetrates in the province of Formosa, alone for about 35 Kms. The non concientización of the problem can cause the loss of the river with the rising desertización of a vast area of the province. The smallest rivers or more outstanding riachos of the province are in the northeast: The Buenos Aires, Black, Salvation, The Pavao, Tatù-Pirè, Big Pretty Mount, Pretty Boy, Argentinean Malvinas, Mount Pilagà, Timbò Porà, and Hè-Hè. In the southeast: San Hilario, Digresses, Formosa, Chestnut, Ramírez, Salted, Short Pick and in the Southwest, The Teuquito. Due to the characteristics of the relief they are plentiful in the province lagoons and tidelands.