Follow a river from its first trickle to its mouth and discover how moving water shapes landscapes along the way.
Explore how rivers begin, join tributaries, carve valleys, form meanders and floodplains, and build deltas as flowing water reshapes the land.
Rivers begin where water gathers from rain, melting snow, glaciers, springs, lakes, or wetlands.
Learn MoreA tributary is a smaller stream or river that flows into a larger one.
Learn MoreFlowing water can loosen and carry clay, sand, gravel, and even large rocks.
Learn MoreAcross flatter land, a river often curves into bends called meanders.
Learn MoreA river's mouth is where it enters an ocean, lake, or another river.
Learn MoreRivers are never truly still.
Learn MoreRivers begin where water gathers from rain, melting snow, glaciers, springs, lakes, or wetlands. A river's source is its starting region, often high in hills or mountains, although some rivers begin on broad plains. Tiny channels join to form streams, and streams combine into larger rivers. The amount of water changes with weather and seasons, so a headwater stream that is gentle in summer may rush strongly during snowmelt or heavy rain.
A tributary is a smaller stream or river that flows into a larger one. Together, the main channel and all its tributaries form a branching river system. The surrounding land that drains water into that system is called a watershed, or drainage basin. Ridges and high ground often separate neighboring watersheds. Because water flows downhill across the whole basin, soil, nutrients, and pollution from far away can eventually reach the main river.
Flowing water can loosen and carry clay, sand, gravel, and even large rocks. This process is erosion. Fast water usually has more power to move sediment than slow water, while tumbling rocks can scrape the riverbed and banks. Rivers transport their load downstream by rolling particles along the bottom, bouncing grains, or carrying fine material in the water. Over long periods, erosion can deepen valleys, cut canyons, and reshape entire landscapes.
Across flatter land, a river often curves into bends called meanders. Water tends to move faster along the outside of a bend, where it erodes the bank, and slower along the inside, where it deposits sediment. The bends can slowly migrate across a wide floodplain. During high water, a river may spill onto this flat land and leave behind fresh sediment. If a meander is cut off, the abandoned bend can become an oxbow lake.
A river's mouth is where it enters an ocean, lake, or another river. When the current slows, it may drop the sediment it has carried. Over time, these deposits can build a delta crossed by smaller channels called distributaries. Not every river forms a delta; strong waves, tides, deep water, or low sediment supplies may carry material away. Some rivers instead widen into tidal estuaries where fresh and salt water mix.
Rivers are never truly still. Floods can move channels, build sandbars, remove banks, and create new habitats in a single event. Droughts reduce flow and expose sediment, while plants and fallen trees redirect currents. Dams, levees, bridges, and channel straightening can also change how water and sediment travel. Studying maps, rocks, soil, and old channels helps scientists understand how a river formed and how it may continue to change.