The Paraná river system is the second largest in South America after the Amazon. It drains an area larger than Greenland: over a million square miles encompassing all of Paraguay and Uruguay as well as big chunks of Brazil, Argentina, and Bolivia. The name of the Paraná River comes from a Tupi Indian phrase meaning “as big as the sea.” But the most interesting thing about the Paraná isn’t its 3,000-mile length. It’s what happens to the river at its mouth.
Where rivers flow into the sea, the result is a delta: a cluster of islands formed from sediment deposited by the river, and a fan-shaped array of tiny waterways passing between then. The network of channels at the mouth of the Nile River was triangular, like the Greek letter delta, and the word eventually came to apply to all such landforms.
The Paraná delta is an 8,400 square-mile maze of river and rainforest, containing over one thousand tiny islands. Locally, it’s called the Tigre region, for the jaguars that once stalked prey there. The Tigre region is just an hour north of Buenos Aires, and today it’s a popular tourist destination. Visitors hop on river cruises to meet the isleños—Tigre locals who live in houses on stilts and buy their groceries on supermarket boats that travel from island to island—and catch a glimpse of colorful tropical birds in one of the world’s great birdwatching spots.
But what makes the Paraná delta unique is its geography. The Paraná doesn’t empty into an ocean or sea, like the Mississippi and the Ganges and the Amazon and all the world’s other great deltas do. The Paraná is the only river delta on earth that empties into another river—in this case, the estuary of the Rio de la Plata. No other river on earth has formed a delta into fresh water.
Another equally unusual kind of river delta to check off your bucket list: the “inland delta.” Sometimes rivers fan out and deposit their sediments not because they’re slowing down as the flow into the ocean, but because they’re drying up. In northern Botswana, the Okavango River spreads out over 5,000 square miles as it flows into the Kalahari Desert. And that’s where the river stops: it never flows out again into any river or ocean. Ten thousand years ago, the area was underwater, as part of an enormous ancient lake called Lake Makgadikgadi, but today the waters of the Okavango fan out, feed plants, and evaporate under the hot African sun.