What has a bed but doesn’t sleep, a mouth but doesn’t speak, and a bank but no money? A river!
Rivers are big, natural flows of water that snake across every continent. They vary widely in size and terrain but share a few basic features.
A river starts with water. That initial source might be a lake or meltwater from snow or ice. As that water flows downhill, precipitation and groundwater add to it. Small streams and creeks merge to form rivers. Rivers can merge to form bigger rivers. Eventually, the river empties into another body of water, such as a lake or ocean. The end of a river is called its mouth.
See all the entries from our Let’s Learn About series
Rivers have immense power to shape the lands they cross. Millions of years of erosion by water from the Colorado River, for instance, sculpted the Grand Canyon. Rivers can also suddenly split or reroute to form new landscapes. This quick change in path is known as avulsion. Where a river meets a lake or ocean, the water can dump sediment to form new land called a delta.
Healthy rivers are important for many reasons. Rivers support aquatic life. That includes invertebrates, fish, plants and more — which can be found throughout a river, from the water’s surface to its bottom, or bed. A river’s water supports plants, animals and other life forms along its banks. People use river water to drink, water crops, transport goods and produce electricity through hydroelectric dams.
But human activity is also harming the world’s rivers.
Runoff from farmland carries pesticides and other pollutants into rivers. Medicines and other chemicals in our wastewater taint rivers as well. Human-caused climate change is warming river waters, stressing species that live there. Dams and groundwater pumping interrupt the flow of water through rivers, damaging their ecosystems. And sometimes people use so much river water that rivers dry up before reaching their mouth.
World Rivers Day — on the fourth Sunday of each September — aims to raise awareness about these threats. Scientists are searching for ways to support and restore these ecosystems. Taking down poorly placed dams and pumping chilly waters into overheated rivers can help. Devising new ways to pull out trash and other pollution are important too.
This World Rivers Day, check out the tools in our Activities section below to get to know the rivers near you. What could you do to help your local rivers thrive?
Want to know more? We’ve got some stories to get you started:
Freshwater fish are in trouble: Here’s how we can help them Human activity can have a huge impact on rivers and other fresh waterways — for good and for bad. (5/22/2025) Readability: 6.9
Pumping cold water into rivers could help fish chill out Human-made cold water plumes could help fish beat the heat as climate change warms rivers. (12/4/2023) Readability: 6.7
Bubbles could help remove trash from rivers An airy curtain of them would divert trash to an onshore collection system. (5/12/2022) Readability: 7.5
Dams were removed along the Klamath River in the U.S. Pacific Northwest in 2023 and 2024. That restored the traditional migration paths for salmon and trout through this region.Explore more
Explainer: Earth’s water is all connected in one vast cycle
Wildebeest drownings feed a river ecosystem for years
Scientist tackles water pollution with epic swims
Climate change is shifting when Europe’s rivers flood
Groundwater pumping is draining rivers and streams worldwide
Antibiotics pollute many of the world’s rivers
A wave of change is coming to our planet’s water resources
Activities
Rivers in different regions boast a huge range of terrains and wildlife. Explore rivers across the United States with on the American Rivers site.
Want to learn more about the health of your local waterways? Check out the How’s My Waterway tool from the U.S. Environmental Protection Agency. You can find the overall conditions of nearby waterways, discover how safe they are for swimming and eating fish, and learn about restoration and protection efforts.
Soil erosion can wash pollutants into rivers and other waterways — but can plants help prevent such land slippages? Find out in this experiment from Science Buddies!
Bengali (Bangladesh) · 
English (United States) ·