The Río de la Plata is a massive estuary on the east coast of South America, forming part of the border between Argentina and Uruguay. Formed by the confluence of the Paraná and Uruguay rivers at Punta Gorda, it empties into the Atlantic Ocean in a broad funnel shape. If classified as a river, it is considered the widest in the world, stretching approximately 290 kilometers in length and widening from roughly 2 kilometers at its head to around 220 kilometers at its Atlantic mouth. The Argentine coast is low-lying and prone to flooding, while the Uruguayan coast to the north is higher, with rocks and dunes.

For paddlers, the most practical and popular access area is around Tigre and San Fernando, located less than an hour north of Buenos Aires. This zone serves as the gateway to the Paraná Delta, an extensive freshwater delta system of rivers, streams, and islands with notable biodiversity. Guided kayak tours operate out of this area, with a base at Boulevard de la Ribera 55 in San Fernando. Tours typically paddle through calm delta waterways before reaching the open waters of the Río de la Plata itself, where views of Buenos Aires are possible. The San Isidro area also provides access to open-water and coastal fishing grounds along the Argentine shore.

The estuary's character changes significantly depending on location. The delta channels offer calm, sheltered paddling, while the open estuary presents a very different environment with shifting currents, variable depths, tidal influences, and weather-driven conditions. The meeting of freshwater and saltwater creates a dynamic habitat supporting diverse aquatic life, including various catfish species. Bird watching is possible in the wetland areas near the delta.

Pollution is a known concern along the Río de la Plata, as waste disposal has historically affected the lowland areas along the Argentine shore. The estuary also carries immense quantities of silt annually, contributing to shoals, banks, and bars. Heavy commercial shipping traffic uses dredged channels through the estuary, including the Punta Indio Channel, which is an important safety consideration for paddlers venturing into open water. Fishing regulations apply in the area, and paddlers should verify any applicable permits before launching.