Río San Javier is a remarkable anabranch of the mighty Paraná River, winding approximately 250 kilometers (160 miles) through the province of Santa Fe, Argentina. Rather than a true tributary, this river functions as a side channel of the Paraná, receiving most of its water from the main stem through a complex network of interconnecting channels. Its source lies on the Paraná River roughly 15 kilometers south of Reconquista, and from there it flows generally southward in a highly meandering and braided course, passing through the towns of San Javier and Helvecia before its mouth empties into a series of channels near Santa Rosa de Calchines — approximately 40 kilometers northeast of Santa Fe City. This intimate connection to the Paraná system means the river shares the rich biological diversity and warm-water fishery that has made the greater Paraná basin legendary among South American anglers.