A rainforest sunset

The Amazon is the largest river in the world by the volume of water it discharges, so powerful that the muddy plume it empties into the Atlantic Ocean covers more than half a million square miles. But it'd be nowhere without its tributaries, the more than 1,000 rivers across nine nations that drain into the Amazon and add to its flow. Across the Amazon drainage basin, which covers about a third of South America, water tends to all end up in one place: the mouth of the Amazon. Take this sunset-tinted lagoon in Ecuador for example—though it's more than 2,000 miles upriver from the Amazon's mouth in eastern Brazil, the waters of the lagoon will slowly but surely empty into the nearby Napo River, which will tumble into northern Peru to meet the rushing Amazon, making its inevitable journey east to the ocean.