The world's weirdest water

There are about 165 major rivers in the world, like the almighty Amazon, the Great Ganges, and the massive Mississippi. But if you were to count every single water flow, from the smallest creek to those immense rivers, it is believed there would be close to three million of them meandering all over the planet. But have you ever wondered what happens when two rivers collide? And what about other weird river phenomena? From rainbow rivers to great gaping holes, grab your life vests, as we're gonna be wading into the weird world of river and water phenomena.

When two become one. Okay, so let's start with the basics. What exactly is a river? While rivers are technically defined as naturally flowing paths of water, not every naturally flowing path of water is a river. Streams, for example, follow more temporary paths, the routes of which can be altered by natural occurrences like rainfall and flooding, whereas rivers, regardless of their size, tend to be carved into the landscape in a route that rarely changes. And thanks to these solidly established paths, rivers provide most of the fresh surface water that we humans access and use. Rivers also transport vital water, minerals, and sediment across the landscape in a vast global network that affects everything from ecology to geography.

You may have heard that all rivers flow into the ocean, but that's a myth. While major rivers often flow downhill towards the sea, some rivers flow straight into other rivers. This is known as a confluence when two or more flowing bodies of water join together to form a single channel. The smaller river that flows into, the larger river is known as a tributary. And the bigger the river, the more tributaries it has.

A clear example is China's incredible Yangtze River, the third longest river in the world. At 3,915 miles long, laid straight, it would be longer than the width of the United States by almost 1,000 miles. It's so big its basin, which is the area of land drained by a river and its tributaries, covers 1/5 of China's total land area. That's a huge amount of land, some 700,000 square miles, which is in part down to the sheer number of tributaries the Yangtze has, more than 700 in total. These tributaries range from small streams to full-blown rivers, such as the Han River, which meanders along 952 miles before it flows into the Yangtze.

But even then, you can still easily tell the two rivers apart as they create this stunning color divide. On the right is the clear blue water of the Han River. While on the left, the Yangtze looks like the whole population of China has dumped their morning tea into it. But that brown stain is actually muddy sediment, like bits of sand, rocks, and dirt, that the river has collected during its journey downstream. While it flows unimpeded, The Yangtze actually carries between 430 and 500 million tons of sediment down its channel every year. That's heavier than all the concrete used to construct the Burj Khalifa, the tallest building in the entire world. This colossal load of sediment makes the water of the Yangtze incredibly dense, and as a result, the clear water of the much shorter Han River can't immediately mix with it, creating this dividing line. Instead, the two rivers flow alongside each other after they meet. Eventually, they mix together further downstream as the sediment gradually disperses.

However, this incredible color contrast isn't just unique to the Yangtze. As you can see, a near-identical effect occurs with the confluence of South America's Inírida and Guaviare Rivers. That's the sediment-rich waters of the Inírida River flowing into the Guaviare River, which itself is a tributary of the Orinoco River. Similar to the Yangtze, the Orinoco is one of the longest rivers in its land, stretching 1,400 miles across Colombia and Venezuela. But we can't talk about big rivers in South America without addressing the almighty Amazon. This gigantic river stretches at least 4,000 miles long, the second longest river on the planet, behind only the Nile River which beats it marginally at 4,132 miles. But while the Nile has more length, the Amazon has more tributaries, with over 1,100 of them feeding into its channel. And with such a large waterway comes some spectacular confluences. Such as here, known as 'the Meeting of Waters,' where the black water of the Rio Negro merges with the sandy Rio Solimoes, yet another tributary of the Amazon River.

Over 3.7 miles, the two rivers run side by side one another without mixing, creating this incredible yin-yang effect. This phenomenon is due to the differences in temperature, speed, and volumes of sediment in the two rivers. Due to the inclines, it runs down, the main River Solimoes flows at a steady 2.5 to 3.7 miles per hour, the average pace of walking. While the Rio Negro, whose channel doesn't follow such a steep incline, is slower at an average speed of 1.2 miles per hour. And it's the river's sluggish pace that also causes its dark-colored water. As the River Negro flows through the surrounding rainforest, vegetation falls in and decays, leaching dark-colored chemical components called tannins into the water. It's the same effect as brewing a cup of tea, but don't get this river's black water confused with your Earl Grey. Because the decayed vegetation makes the water highly acidic, with a pH high of 2.9, equivalent to the acidity of grapefruit juice. Probably tastes as gross too.

While that sounds dangerous, confluences, such as the Meeting of Waters, are vital for wildlife because this color clash mixes up nutrients in the water. In fact, along the Rio Solimoes' 1,000-mile length, the diversity of electric fishes, such as eels and catfish, increases closer to confluences due to the increased richness of nutrients and organic matter. Still, with lightly acidic waters and electrical animals, I wouldn't dip your toes into the Meeting of Waters.

But depending on activity in the surrounding basins, the rivers can appear in a variety of different colors when they meet. Such as here, where the clear water from Granite Creek flows into the muddy seen here comes from landslides that happened further upstream, giving its waters an even greater makeup of sediment. Or here, at the color-clashing confluence of the Rhone and Arve Rivers in Switzerland. The deep blue of the River Rhone clashes with the denser milky green water of the River Arve, which is full of white sand sediment.

But the best things always come in threes, as the famous Passau confluence demonstrates. Located on the German-Austria border, this is where several rivers combine with amazing triple colors. The thinner, darker stream on the far side is the River llz. Its basin contains the Bavarian forest of Germany, collecting decayed plant debris and peaty soil from the surrounding forest. The river llz and the lnn are both tributaries feeding into the river Danube in the center.