A SPRING AFTERNOON AND EVENING AT DOS RIOS The preparations for a visit to Dos Rios always follow a similar pattern, particularly packing up the cool box. What might one forget? Did we leave wine, vodka, and lemons from the last visit? The caretaker Beto picks us up from the dock on the mainland – sometimes the water is like silk, sometimes it is choppy from all the passing boats if lovely weather beckons the Porteños out to the Delta. Boats of all shapes and sizes bob and rush about on the river, and a…