MANAUS, BRAZIL - Within the metropolitan region of Manaus lies one of the most famous natural phenomena of the Brazilian Amazon: the “Meeting of the Waters” of the Solimões and Negro rivers, which occurs near the capital of Amazonas state. This natural wonder stretches for roughly six kilometers without the mixing of the two rivers, forming a visible line that can be seen even from above.

To understand what causes this phenomenon, we invited geographer Marcos Castro, from the Federal University of Amazonas (UFAM), to explain what fascinates both local residents and the many travelers who visit the region.

Marcos Castro, geographer – Federal University of Amazonas (UFAM)
“This separation between the waters is caused by physical and chemical factors. For example, river flow is a physical factor: the flow velocity of the Solimões–Amazon River is higher than that of the Negro River. In terms of chemistry, the Negro is a more acidic river, with a pH that ranges from 3.5 to 5.5, while the Amazon River’s pH, which is nearly neutral to slightly alkaline, ranges from 6.5 to 7.5. So, this is a chemical division of the waters. Flow velocity and temperature also play a role, which makes it a physico-chemical separation. You have both chemical and physical components contributing to this phenomenon, preventing the waters of these two giants from mixing,” Castro said.

“The Negro River, being more acidic, also carries a significant amount of decomposing organic material from the surrounding forests. Since it is also an older river, its riverbed is more deeply carved, and it transports iron-rich sediments from the rocks. This combination of iron and decomposed vegetation results in the river’s dark, almost black color. The Amazon River, on the other hand, carries sediments from its own margins, making it rich in suspended particles, which gives its waters a kind of milky brown coloration,” the geographer explained.

“The tourist appeal is enormous. People come from all over the world to witness this spectacle, because it truly is a natural marvel — two hydrological giants that do not mix. Visitors can come especially on clear days like today, when the sky is wide open and the sun is high. That’s the best time to visit, because the sunlight over the water makes the contrast of the meeting much sharper,” said Marcos Castro of the Federal University of Amazonas (UFAM).

www.amazonagency.noticias