This phenomenon is due to the differences in temperature, speed, and amount of dissolved sediments in the waters of the two rivers. The Rio Negro flows at near 2 km/h (1.2 mph) at a temperature of 28 °C (82 °F), while the Rio Solimões flows between 4 and 6 km/h (2.5–3.7 mph) at a temperature of 22 °C (72 °F).
All rivers flow to the oceanExcept for the driest deserts, every place on Earth has a connection to the ocean through a river. Even the highest mountain in the world, Mt. Everest, is connected to the sea by flowing water. Because of their connectivity, rivers gave rise to human civilization.
It always does — right? But under Antarctica's ice, water can sometimes run uphill. Under the right conditions, a whole river can spurt from one lake uphill to another lake. That's because the ice weighs so much that it presses down on the water with thousands of pounds of pressure per square inch.
Why the Tonle Sap River Is Unlike Any Other River in the World. In this week's Maphead column, Ken Jennings explains how one river in Cambodia ends up changing direction a few times every year.