This phenomenon is something that you need to see. In Manaus, that is the largest city in the Amazonas, there are two rivers that literally meet each other. The rivers are Rio Negro and the Amazon, and they have completely different colors, so when the phenomenon happens you can see the contrasts from the water.
They call it “The Meeting of the Waters”, and in Portuguese that would be” Encontro das Águas”. It is certainly a huge tourist attraction, and every year they jump on boats to have a look at the beautiful “fusion”. You can say that Rio Negro has an almost black color, while the Amazon is more of a sandy color.
Their temperature are also different, and their speed of how fast they are floating, so this all makes perfect conditions for the phenomenon. And the split ranges over four kilometers so when you are there you probably won’t miss it. Another nature phenomenon that includes water is the Eaglehawk Neck.