Rio das Antas is a significant river in the state of Rio Grande do Sul, in southern Brazil, forming the upper portion of the Taquari-Antas river basin — one of the main sub-basins of the Patos Lagoon drainage system, which ultimately flows into the Atlantic Ocean. The river originates on a high basaltic plateau at elevations ranging from approximately 800 to 1,200 meters above sea level, then carves through deeply incised valleys as it descends toward the lowlands, where it transitions into the Taquari river. The basin covers a total area of 26,470 km², making it a substantial watershed with diverse aquatic habitats ranging from fast-moving highland streams to broader, lower-gradient reaches. The region has been shaped by a combination of natural basaltic geology and significant human activity, including agriculture, urban development, and an extensive network of hydroelectric power plants — with 26 facilities ranging from less than 1 MW to 130 MW in operation or under construction in the broader basin as of the early 2010s.