Rather than instantly intermingle, when these two rivers meet, they need time to get to know each other before becoming one.
Question: What natural phenomenon smack in the middle of the Amazon is visible from space?
Answer: The meeting of the waters in Manaus, Brazil
When you hear the term Amazon River, you may picture a single, vast torrent, but it is actually several rivers that eventually become one. What is most often considered the upper Amazon is the Rio Solimões, which flows from northern Brazil on its way to the Rio Negro, which originates in Colombia. When eventually they meet, in Manaus, they become the powerhouse lower Amazon.
But before they truly unite, it becomes clear just how different these rivers really are. The Solimões is pale and sand-colored; the Negro is named for its black water. And instead of instantly blending, the two rivers run for four or five miles notably divided along a distinct line: dark water to one side, light water to the other.
The fact is the rivers are like strangers meeting and realizing they don’t speak the same language. The seemingly dark waters of Rio Negro are actually crystal clear, flowing just over a mile an hour in speed, and maintaining a balmy 82 degrees in temperature. Rio Solimões on the other hand is sand-colored because it is full of sediment, and it is a full ten degrees cooler than the Solimões. Meanwhile, it’s more than three times as fast. As a result, when the rivers meet, it takes time for them to adjust to coexistence and finally blend into a unified lower Amazon.
The view is spectacular whether you witness it from land or boat. And that’s not limited to viewers on earth: The contrast between rivers is so dramatic that the color line was discernible to the crew of the Space Shuttle Endeavor when it passed overhead.
Rio Negro by the Numbers
- The Rio Negro is the largest blackwater river on earth, running 1,400 miles, only a third of which are navigable.
- Its basin occupies an area of 267,000 square miles (about the size of Texas).
- It is one of the ten largest rivers in the world when measured by discharge (nearly a million cubic feet per second).
- It is responsible for roughly 15% of the water in the Amazon basin.
- The Rio Negro basin is fed by as much as 130 inches of rain per year.
- The water is not pleasant for drinking; at 2-4pH levels it is highly acidic (which makes for a metallic or sour taste).
- In rainy season, the Rio Negro is 19 miles across at its widest point.
- The water level fluctuates from 10 feet to more than 30 feet deep.
- There are 600 islands in the river, including one archipelago spanning nearly 900,000 acres just above the meeting of the waters.
- The river is home to more than 700 documented fish species, including 100 endemic to Rio Negro, and another 20 that have not yet been classified.
Witness this natural phenomenon for yourself on our Brazil: Manaus & the Amazon Rainforest pre-trip extension before your Exploring South America: Rio, Buenos Aires, Patagonia & Chilean Fjord Cruise.