Introducción:

Within the metropolitan area of Manaus lies one of the most renowned natural phenomena of the Brazilian Amazon: the Meeting of the Waters, where the Solimões and Negro rivers run alongside each other near the state capital. This natural spectacle stretches for about six kilometers without mixing, forming a sharp, visible line even from above.To understand the causes behind this occurrence, we spoke with geographer Marcos Castro from the Federal University of Amazonas (UFAM), who explains the phenomenon that captivates local residents and the many travelers who visit the region.

Duración: 08'35"

Interviews:
Marcos Castro – Geographer, Federal University of Amazonas (UFAM)

Interno:
Fernanda Soares

Editing and Post-Production:
Alexandre Almeida

Producción ejecutiva:
Juliana Fontes

Producción:
AGENCIA AMAZON
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**Guion**
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– Opening track

“The Meeting of the Waters goes far beyond the difference between the waters of two of the world’s major rivers, the Rio Negro and the Rio Solimões, which from this point on—at the Meeting of the Waters—becomes the Amazon River.”

– Audio track

Marcos Castro – Geographer, Federal University of Amazonas (UFAM)

“This separation of waters is a physico-chemical division. For example, speed is a physical factor: the Solimões–Amazon River flows faster than the Rio Negro. In chemical terms, the Rio Negro is a more acidic river; its pH ranges from about 3.5 to 5.5, while the Amazon River’s pH—nearly neutral to alkaline—varies from 6.5 to 7.5. So this is a chemical division of the waters. Speed and temperature also differ, forming a physico-chemical divide. Here, both chemistry and physics contribute to the phenomenon that prevents these two giants from mixing.”

– Audio track

“This combination is what makes the waters so different and prevents the rivers from mixing, creating the natural spectacle known as the Meeting of the Waters. It’s worth noting that it’s not only about water color; it also represents two distinct Amazon worlds. The Solimões side is more populated and is known as a várzea river—its floodplains dominate the landscape, and human occupation is much greater there due to the more fertile soil. In contrast, the Rio Negro is older, has less fertile soils, and its banks are less occupied than those of the Solimões–Amazon River.”

– Audio track

“Because the Rio Negro is more acidic, it also carries many decomposing sediments from the surrounding forests. Being an older river, its channel is more deeply carved, and it transports ferruginous sediments—iron from rock formations. This combination of iron and decomposed vegetation results in the river’s dark, almost black, water. The Amazon River, on the other hand, carries sediments from its own banks, which remain in suspension and give the water its characteristic glacé-brown color.”

– Audio track

“Outside urban areas, the Amazon River is heavily inhabited, even though it floods and submerges its banks. Many cities and communities experience inundation. However, despite this apparent challenge during the flood season, the dry season leaves extremely fertile soil enriched with potassium and magnesium. This allows riverside communities to practice productive agriculture—something that does not occur along the Rio Negro. Because the Rio Negro is more acidic and lacks periodic flooding, its soil undergoes a process known as leaching, meaning nutrients are washed away from the surface, leaving poorer soil behind.
Each river has its advantages and disadvantages. For example, the Rio Negro has very few mosquitoes—the borrachudos or carapanãs, as they’re called in the Amazon—while the Solimões has many. Why? Because the Rio Negro’s acidity prevents mosquito proliferation, whereas the Amazon River’s less acidic, nearly neutral to alkaline water allows them to thrive—an obvious disadvantage. Yet in terms of human settlement, the Amazon River is more heavily occupied because its soil is richer and better suited for agriculture.”

– Audio track

“The Solimões–Amazon River originates in what is called the pre-Andean region, in the Peruvian foothills. As it flows inward, it is known as the Marañón until it reaches Brazil, where it becomes the Amazon River. It’s important to remember that the entire stretch, from source to mouth, is technically the Amazon River, but regional naming conventions apply. From Manaus upriver to the Peruvian border, it is called the Solimões. From the Meeting of the Waters to the river’s mouth, it is called the Amazon. But scientifically speaking, the whole river is the Amazon.
The Rio Negro rises on the Guiana Shield, across Brazil, Venezuela, and Colombia. It is a different geological formation. It meets the Amazon here, in front of Manaus, and the two flow side by side for nearly six kilometers until the Amazon’s waters fully dominate downstream.”

– Audio track

“There are several Meetings of the Waters in the Amazon. For example, in Santarém, the Amazon River meets the Tapajós River, creating another massive confluence. Here in Amazonas state, the Amazon River also meets Lake Coari, which has dark waters similar to the Rio Negro. Other examples include Tefé and Parintins—particularly a stretch called Paraná do Ramos—which also feature these water confluences.
This natural spectacle occurs in many parts of the region, but this one is the largest—not only because it unfolds beside Manaus, the biggest metropolis in the Amazon, but also because of the sheer scale of the two rivers: the Amazon, the world’s largest river by volume, and the Rio Negro, also one of the world’s largest in both length and width.”

– Audio track

Marcos Castro – Geographer, Federal University of Amazonas (UFAM)

“The appearance of the Meeting of the Waters has been changing recently. The island of Xiboréna, right behind me, has been expanding due to sediment deposition. Meanwhile, on the opposite side, Careiro Island is under hydrostatic pressure. A lake there, known as Lake Joanico, has already begun to disappear. This deposition and pressure create an erosion process that gradually reshapes the Meeting of the Waters. Fortunately, the spectacle itself is not at risk of disappearing.”

– Audio track

“The Meeting of the Waters is a protected area. It is a designated natural heritage site belonging to the people of Amazonas, to Brazil, and, I would say, to humanity.”

– Audio track

“The tourist appeal is immense. People from all over the world come to witness this spectacle because it truly is remarkable—two hydrological giants that do not mix. The best time for visitors is on days like today, when the sky is clear and the sun is high. The sunlight enhances the contrast on the water, making the meeting line stand out vividly.”

– Final audio track