Arroyo Fortaleza is a clear-water stream flowing through the subtropical forests of Misiones Province, Argentina, draining into the río Uruguay basin. This relatively small but ecologically rich arroyo is characterized by irregular depths averaging around 80 centimeters, a substrate of sand and stones, and a course punctuated by small waterfalls and pools. The water runs clear and free of aquatic vegetation, with temperatures typically ranging between 24–25°C. The surrounding riparian zone reflects the dense native forest of Misiones, making it a visually striking and biologically diverse fishing destination. The stream sits within the headwater zone of the río Uruguay drainage, and its combination of falls, pools, and varied substrate creates a mosaic of microhabitats that support a distinctive assemblage of native fish species.