The Rio das Antas flows approximately 390 kilometers through Rio Grande do Sul, originating in the municipality of São José dos Ausentes within the Aparados da Serra National Park at an elevation of around 1,200 meters. It travels westward across the state until it joins the Rio Carreiro near Bento Gonçalves and São Valentim do Sul, at which point it takes on the name Rio Taquari.

The river's character varies considerably along its length. The upper and middle sections are turbulent with an absence of floodplains, giving the river a more dynamic, fast-moving nature. This stands in contrast to the lower Taquari, which below the city of Muçum becomes generally navigable with broad várzeas. The turbulent regime of the Rio das Antas proper makes it more suited to paddlers comfortable with moving water conditions.

The river passes through the Serra Gaúcha region, with paddling activity in the area around Caxias do Sul, including near a landmark known as Ponte dos Korff. The surrounding landscape reflects the elevated plateau terrain of the Planalto dos Campos Gerais in the upper reaches, transitioning as the river descends toward the lowlands.