Separated from the Paraneña region by the Río Paraguay, the Chaco region is a vast plain with elevations reaching no higher than 300 meters and averaging 125 meters. Covering more than 60 percent of Paraguay's total land area, the Chaco plain gently slopes eastward to the Río Paraguay. The Gran Chaco, the entire western portion of the region, is subdivided into the Alto Chaco (Upper Chaco), bordering on Bolivia, and the Bajo Chaco (Lower Chaco), bordering on the Río Paraguay. The low hills in the northwestern part of the Alto Chaco are the highest parts in the Gran Chaco. The main feature of the Bajo Chaco is the Estero Patiño, the largest swamp in the country at 1,500 square kilometers.
Data as of December 1988