Río de la Plata Coast

The Uruguayan shore of the Río de la Plata estuary runs from the Argentine border near Fray Bentos east to Montevideo, where the coast turns to face the Atlantic proper. This is a freshwater-influenced, sediment-laden, wind-dominated tidal regime very different from the open-ocean coasts of Rocha. The Río de la Plata is the world's widest river estuary — 220 km across at its mouth between Punta del Este and Buenos Aires — and the water varies from nearly fresh near the Paraná delta to brackish near the ocean mouth. Colonia del Sacramento on the northern shore sits at a relatively saline part of the estuary, where the tidal signal (0.8 to 1.0 m semidiurnal) is detectable but wind setup regularly dominates. Southerly storms push water northward into the estuary; the resultant surge can exceed 1.5 m above predicted level in Montevideo and along the northern shore. Historic Colonia's ferry crossing to Buenos Aires is the most direct route between Uruguay and Argentina, taking about an hour. Predictions come from Open-Meteo Marine, accuracy class ±45 min / ±0.2–0.3 m.