Arroyo Ayuí Grande is a stream winding through the Entre Ríos Province of Argentina, positioned at approximately 31°17′S, 57°57′W in the western reaches of this richly biodiverse province. The stream flows through the characteristic subtropical lowland landscape of Entre Ríos, where dense riparian vegetation lines the banks and the warm, slow-moving waters support a diverse community of native South American fish species. This is classic warm-water stream fishing in the heart of Argentina's Mesopotamia region, offering anglers the chance to pursue some of the most exciting and hard-fighting freshwater species on the continent.