There are two main currents in the province, with a very well defined drainage net, and numerous small flows. Besides there is a Lacustrine system in the west. The rionegrina hydrography contains two slopes, one from the Atlantic Ocean, and the other from the Pacific Ocean and Lakes. The main rivers of the Atlantic slope are:
Río Colorado: it is located in the north, constituting the limit between Río Negro and La Pampa. Its bed is to the southeast, except near Colonia Catriel. Its waters are cloudy due to the erosion of the rivers that form it. Basaltic mountains of up to 100 meters height go along it, until they gradually disappear to become low and sandy terraces. The river's width oscillates between 100 and 300 meters. Valley's walls distanced up to 4 kilometers in some tracts, are a clear proof that it had a strong erosive power. It doesn't receive flowings, that is why its flow diminishes progressively. The final tract presents a delta form. It drains in the Atlantic Ocean, forming a low coast, full of sand dunes and very arid.
Río Neuquén: it constitutes the limit between the Neuquén and Rio Negro Provinces. This river has 510 kilometers length, it is quick, and drafty, just as its Araucanian name says. It means audacious and arrogant. It receives many tributaries that gather the abundant Andean rains. To the south and next to its final tract, it is the Vidal basin and the Ballester dike.
River Limay: It starts at Nahuel Huapi Lake and it defines the limit between Neuquén and Río Negro Provinces. It has 430 kilometers length and along its flowing it saves 508 meters difference. A lot of lakes interposed in its basin make it more regular, less impetuous and less quick than Neuquén River. This river receives its bigger tributaries of the neuquino sector, in Río Negro Province it has only two tributaries, the Pichileufú and Comallo Rivers and some temporary streams. Near Picún Leufú in Neuquén, the river becomes an artificial lake, forming El Chocón dam. It contributes to form most of the flow of Negro River.
Río Negro: It is the most important province's collector. It is formed by the confluence of Neuquén and Limay Rivers. It has 635 Kilometers length until its Atlantic Ocean outlet. It takes a flow of 1.000 cubic meters per second. The Valley's width varies along its flow, there are some tracts of about 20 kilometers and some others of about 3 kilometers. In Alto Valle and Valle Medio, the thatched tops that surround it are very high. Along the half tract it opens in two branches, determining a series of islands, the biggest one is Choele Choel Grande. In the inferior tract its flow gives place to a lot of bends, appearing secondary branches. The Río Negro is the third river of Argentina due to its longitude, flow and navigability. It presents two yearly floods which are the result of the combined regimens of Neuquén and Limay Rivers. One is in winter, in July, caused by the rains, and the other is in spring, in September, originated by the snow thaw.
River Chubut and Azul: they start in Río Negro Province. The Azul River takes its waters to the Puelo Lake, integrating the Mauso's system. The Pacific slope has only one river, Manso, that starts in the Tronador Hill and presents in its basin thirteen lakes, among them the Mascardi, Guillelmo, Fonk, Steffen and Martin. In Chile, it joins Puelo River.
The Lakes : They are located in the Andean area, originated by the glacier's action, they are deep, lengthened, they are fed by thaws and the abundant precipitations. Nahuel Huapi lake, shared by Neuquén and Río Negro provinces, is characterized by its depth and branches. It has a surface of 500 square Kilometers and it has islands and cold blue transparent waters. Other important lakes are Gutiérrez, Mascardi, Marín and Steffen.