The Bug River, in Poland (Photo: Wikimedia Commons)
A river is a large stream of water that flows in a channel toward a lake, ocean or sea. Usually consisting of freshwater, the water in rivers can come from precipitation, surface runoff, springs, glacial melting, groundwater discharge, or a blend of these processes. While most rivers flow on the surface of the Earth, some flow in caves and caverns; these are known as subterranean rivers. Rivers are a key component in various planetary cycles.
Rivers have been a crucial part of life on Earth since time immemorial. They serve as ecosystems for fish, plants, bacteria and other wildlife. Humans and animals alike use them as sources of drinking water, bathing and food. Humans also use rivers as energy sources in the way of hydropower and as major passageways of transport or navigation. Rivers have even had political influence — many have served as borders of countries and the landforms often act as defensive measures in theaters of war.
Rivers are currently in a state of crisis for several reasons. Building dams and levees help humans but they impair life in the riverine ecosystems and disrupt planetary processes. As a result, many rivers have degraded and some no longer reach the oceans they once did. Moreover, pollution from a variety of sources has diluted (and in some cases, even poisoned) the water that rivers carry. This has harmed the populations found inside rivers and the humans who drink from them. (Photo: Wikimedia Commons)

A mudlark explains the joy of her river hobby

9 interesting facts about the Nile River

Mysterious blind 'ghost fish' reveals Congo to be the deepest river in the world

With dam removed, Green River flows freely

What is the Gulf of Mexico dead zone?

The surprising beauty and benefits of driftwood

How London's 'lost' underground rivers could help curb carbon emissions

Tucson to resurrect river with recycled water

Why do rivers need riverkeepers?

Great Amazon Reef System is larger than previously thought

Gigantic lily pads reappear in Paraguay lagoon

Rare seahorses discovered in the River Thames