Meeting of Waters (Manaus)

Just downstream from Manaus, two of the great rivers of the Amazon basin meet and, for a few kilometres, refuse to become one. The Rio Negro arrives nearly black, the colour of strong tea, stained by decayed leaves and plant matter from the forests it drains and carrying almost no sediment. The Solimões - the name Brazilians give to the upper Amazon - comes in pale and sandy, loaded with silt washed down from the Andes. Where they join, a sharp seam runs down the middle of the water, and for about 6 km the two streams travel side by side, dark against light, before finally blending into the single river that continues to the Atlantic.

The reason the line holds is physical, and it is one of the most visible lessons in hydrology anywhere. The Negro is warmer, around 28 degrees, while the Solimões runs at about 22; the Negro moves slowly, near 2 km/h, while the Solimões flows at 4 to 6 km/h; and their loads of sediment give them different densities. Warm, slow, clear water slides against cold, fast, muddy water, and the boundary survives far longer than intuition suggests. From a boat you can see small whorls and tongues of each colour curling into the other along the edge, and trailing a hand in each side makes the temperature difference easy to feel.

The phenomenon is not unique - smaller versions occur elsewhere in the Amazon, at Santarém and in Peru - but none is as large or as close to a city. In November 2010 Brazil's national heritage council voted unanimously to protect it as a landscape, covering ten continuous kilometres of the meeting and about thirty square kilometres around it. Oscar Niemeyer drew up a monument for the site as one of his last projects; it was never finished.

The best way to understand the scale is from the water in the middle of the day, when the contrast is sharpest, when the two ribbons of colour stand out most clearly against each other.

Getting there

The meeting point lies a few kilometres east of central Manaus and about 11 km from Careiro da Várzea on the opposite bank. Eduardo Gomes International Airport (MAO), which serves Manaus, is about 19 km away. Boat tours leave from Manaus, many of them from the Ceasa port on the city's eastern edge, around half an hour by road from the centre. The public ferry from the Ceasa port to Careiro crosses the confluence and gives a good view of it.