The Pantanal () is a natural region encompassing the world's largest tropical wetland area, and the world's largest flooded grasslands. It is located mostly within the Brazilian state of Mato Grosso do Sul, but it extends into Mato Grosso and portions of Bolivia and Paraguay. It sprawls over an area estimated at between . Various subregional ecosystems exist, each with distinct hydrological, geological and ecological characteristics; up to 12 of them have been defined. Roughly 80% of the Pantanal floodplains are submerged during the rainy seasons, nurturing a biologically diverse collection of aquatic plants and helping to support a dense array of animal species. Etymology The name "Pantanal" comes from the Portuguese word pântano that means "big wetland", "big bog", "big swamp", "big quagmire" or "big marsh" plus the suffix -al, that means "abundance, agglomeration, collection"; By comparison, the Brazilian highlands are locally referred to as the planalto, that means "plateau" or, literally, "high plain". Geography and geology The Pantanal is about , gently-sloped basin that receives runoff from the upland areas (the Planalto highlands) and slowly releases the water through the Paraguay River and tributaries. The formation is a result of the large, concave pre-Andean depression of the earth's crust, related to the Andean orogeny of the Tertiary. It constitutes an enormous internal river delta, in which several rivers flowing from the surrounding plateau merge, depositing their sediments and erosion residues, which have been filling, throughout the years, the large depression area of the Pantanal. This area is also one of the distinct physiographic provinces of the larger Parana-Paraguay Plain area, which encompasses a total of . The Pantanal is bounded by the Chiquitano dry forests to the west and northwest, by the Arid Chaco dry forests to the southwest, and the Humid Chaco to the south. The Cerrado savannas lie to the north, east and southeast. The Pantanal is a tropical wet and dry region with an average annual temperate of and rainfall at a year. Throughout the year, temperature varies about with the warmest month being November (with an average temperature of ) and the coldest month being June (with an average temperature of ). Its wettest month is January (with an average of ) and its driest is June (with an average of ). Hydrodynamics Floodplain ecosystems such as the Pantanal are defined by their seasonal inundation and desiccation. They shift between phases of standing water