Mississippi River on the border between Arkansas and Mississippi, USA

We are looking down on the border between Arkansas and Mississippi in the United States. This image was taken by a satellite, and those small, blocky shapes are towns and fields. The twisting blue-green colour is the Mississippi River, which is one of the longest and most famous rivers in the world. It flows over 3,700 kilometres and is so long that it takes 90 days for a drop of water to travel the whole length of the river. It runs through 10 states and has been a very important route for trade and travel for centuries.
© NASA