The Negro River, as its name suggests, is a river with very dark waters. Its black tea color is due to the large amount of organic acids from plant decomposition.
It has a high degree of acidity, with a pH of 3.8 to 4.9, and an average temperature of 28º C, and it flows slowly.
The Solimões River, on the other hand, has a muddy color very similar to coffee with milk. All this because of the large number of sediments that the water carries as it flows under the Andes Mountains.
It is colder than the Negro River, at 22º C. In addition, it flows much faster, running about 6 km per hour.
The Meeting of the Waters is the meeting of the Negro and the Solimões rivers, which, initially, do not mix. This phenomenon extends for about 6 km. After they come together, they are renamed the Amazon River, one of the main economic and transport means for the inhabitants of the city of Manaus.
The difference in composition, acidity rate, flow temperature and density is what prevents the two from mixing together at first when they meet. The color contrast is very stark and can even be seen from space. Sometimes the water encounters obstacles that form strong eddies that stir the two rivers and make very beautiful shapes.
Source: Mega Curioso