Río San Antonio flows through the Buenos Aires province of Argentina as part of the intricate network of waterways that defines the Paraná Delta and surrounding river system. This river sits within a broader web of interconnected channels, streams, and tributaries that collectively form one of South America's most productive freshwater fishing environments. The waterway shares its ecosystem with notable neighboring rivers including the Río Luján, Río Tigre, Río Reconquista, and Río Paraná Miní, placing it squarely within a region celebrated among Argentine anglers for its diversity of species and accessible fishing opportunities.