Question: The Mocoví are an indigenous tribe of a sparsely populated region of what basin?

Context paragraphs:
Middle Fork Eel River: The Middle Fork Eel River is a major tributary of the Eel River of northwestern California in the United States.  It drains a rugged and sparsely populated region of the Yolla Bolly Mountains, part of the California Coast Range, in Trinity and Mendocino Counties.  Its watershed comprises roughly 745 mi2 of land, or 20% of the entire Eel River basin.  The river provides groundwater recharge and is used for recreation and for industrial, agricultural and municipal water supply by residents.

Cyclone Monty: Severe Tropical Cyclone Monty was a powerful category 4 tropical cyclone that formed during late February 2004.  Monty was the 6th tropical cyclone and the 3rd Severe tropical cyclone of the 2003-04 Australian region cyclone season.  Monty made landfall in a large, sparsely populated region of the Pilbara, Western Australia.  Due to the low population, damages inland were not high, although there was major flooding and many roads were impassable because they were flooded or washed away by water.  Monty set record high amounts of flooding in some parts of Western Australia.

Mocoví: The Mocoví are an indigenous tribe of the Gran Chaco.  They speak the Mocoví language.

Cyclone Lua: Severe Tropical Cyclone Lua affected a sparsely populated region of Western Australia during mid-March 2012.  Originating in a broad low pressure area that formed northwest of Australia by 8 March, the storm was plagued by inhibiting wind shear for the duration of its formative stages.  However, it gradually organized, and received the name Lua on 13 March.  The cyclone meandered for the first several days of its existence, caught between weak and competing steering currents.  After the cyclone drifted northwestward, a building ridge of high pressure to the north drove Lua southeastward toward the Pilbara region.  Ultimately intensifying into an upper-end Category 3 severe tropical cyclone with maximum sustained 10-minute winds of 155 km/h (100 mph), Lua made landfall near the remote community of Pardoo, about 150 km (95 mi) east of Port Hedland.  It steadily weakened as it progressed south over interior Western Australia, diminishing below tropical cyclone status on 18 March.

Gran Chaco: The Gran Chaco (Quechua: "chaku", "hunting land") is a sparsely populated, hot and semi-arid lowland natural region of the Río de la Plata basin, divided among eastern

Patagonia: Patagonia (] ) is a sparsely populated region located at the southern end of South America, shared by Argentina and Chile.  The region comprises the southern section of the Andes mountains as well as the deserts, pampas and grasslands east of this southern portion of the Andes.  Patagonia has two coasts: western facing the Pacific Ocean and eastern facing the Atlantic Ocean.

Aysén Region: The XI Aysén del General Carlos Ibáñez del Campo Region (Spanish: "Región de Aysén" ] "XI Región Aysén del General Carlos Ibáñez del Campo "), often shortened to Aysén Region or Aisén, is one of Chile's 15 first order administrative divisions. Although the third largest in area, the region is Chile's most sparsely populated region with a population of 102,317 as of 2017.  The capital of the region is Coihaique, the region's former namesake.

Mid West (Western Australia): The Mid West region is one of the nine regions of Western Australia.  It is a sparsely populated region extending from the west coast of Western Australia, about 200 km north and south of its administrative centre of Geraldton and inland to 450 km east of Wiluna in the Gibson Desert.

Say Department: Say is a department of the Tillabéri Region in Niger.  Its capital city is Say, and includes the towns of Guéladjo, Tamou, and Torodi.  It abuts the urban Region of Niamey, and lies across the Niger River to the southwest of the capital.  It extends to the Burkina Faso border over 60 km to the west, and the northernmost border with Benin in the south.  The Say area is today divided between the riverine valley in the east of the Department, and the more sparsely populated areas to the west, which are intercut with a series of eastward flowing tributaries.  The Niger river, a broad shallow channel at Niamey and at Say, passes through a series of gorges and cataracts, called the "W" bend for the shape the river takes, in the south of the Say Department.  To the west of these rapids lies what is now the W Regional Park, a sparsely populated area historically plagued by insect borne diseases of both humans and cattle.  Now a park and tourist attraction, its history as a "no mans land" has made it a refuge for remaining wild animals, as well as several undisturbed archeological sites.  From at least the 16th century CE, the Zarma people moved south into this area from the northern plateau around what is now Oullam.  The inhabitants at the time were related to the Gourma people, who form most of the population of the northwestern part of the Department today.  In the 18th and 19th century, the town of Say was founded by Fulani migrants from the Gao region of modern Mali, with others expanding from what is now northeast Burkina Faso.  Between 1810 and the arrival of European writer Heinrich Barth in 1854, Fulani Muslims led by Alfa Mohamed Diobo of Djenné had established the Emirate of Say.  The reputation for piety and learning of Mohamed Diobo and his followers helped turn Say from a small river village into a town of 30,000, famed across West Africa as a center of learning.

Racha-Lechkhumi and Kvemo Svaneti: Racha-Lechkhumi and Kvemo Svaneti (Georgian: რაჭა-ლეჩხუმი და ქვემო სვანეთი , "Raç̇a-Leçxumi da Kvemo Svaneti") is a region (Mkhare) in northwestern Georgia which includes the historical provinces of Racha, Lechkhumi and Kvemo Svaneti (i.e., Lower Svaneti).  It covers an area of 4,954 km² and has a population of 31,927 (2014 census), but nominally also a section of northwest South Ossetia, over which Georgia has no jurisdiction and control.  It is the most sparsely populated region in the country.  The capital is Ambrolauri.

Supporting paragraphs: Mocoví Gran Chaco
Answer: Río de la Plata basin