A river is a large, natural stream of freshwater that flows across land, usually from higher ground to lower ground, eventually emptying into an ocean, sea, or lake. Rivers start small, often as springs or mountain streams, then grow wider and deeper as smaller streams called tributaries join them along the way.

Rivers have shaped human civilization for thousands of years. Ancient Egypt developed along the Nile River. Major cities like London, Paris, and New York grew up beside rivers because the water provided transportation, power for mills, drinking water, and irrigation for crops. Before highways and railroads, rivers were nature's highways, letting people move goods and travel long distances.

The word river can also describe anything flowing in large quantities. You might say tears streamed down someone's face in rivers, or that rivers of lava flowed from a volcano. When rain pours down your windshield, it might run down in rivers.

Rivers come in all sizes, from the mighty Amazon (the world's largest by volume) to smaller rivers you could wade across. Each river has a personality shaped by the landscape it travels through: some rush fast and wild through mountains, while others meander slowly and peacefully through plains. The current (the flow of water) can be gentle or powerful enough to carve canyons through solid rock over millions of years.