Meeting of the Waters (Encontro das Aguas)

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The confluence a short distance downstream of Manaus where the black Rio Negro meets the pale, sediment-laden Solimoes and the two run side by side, visibly unmixed, for several kilometres before merging. It is the clearest single demonstration in the basin that a river is not one substance. The Negro drains the deeply weathered Guiana Shield: nutrient-poor, acidic, stained by dissolved organic compounds, warm and slow. The Solimoes carries suspended Andean rock flour: cooler, faster, denser, and far richer in the mineral nutrients that make its floodplains fertile. The difference in density, temperature and velocity is what delays mixing. The forests either side differ accordingly, and so does the fish fauna - which is why a purely hydrological curiosity is also an ecological boundary.