This is a picture of the Colorado River near Hoover Dam.
Click on image for full size
Rivers are very important to Earth because they are major forces that shape the landscape. Also, they provide transportation and water for drinking, washing and farming. Rivers can flow on land or underground in deserts and seas. Rivers may come from mountain springs, melting glaciers or lakes.
A river's contribution to the water cycle is that it collects water from the ground and returns it to the ocean. The water we drink is about 3 billion years old because it has been recycled over and over since the first rainfall.
A delta is where a river meets the sea. Usually the river flows more slowly at the delta than at its start because it deposits sediment. Sediment can be anything from mud, sand and even rock fragments. A special environment is created when the fresh water from the river mixes with the salty ocean water. This is environment is called estuary.
The longest river is the Nile River in Africa, and the Amazon River in South America carries the most water. The muddiest river is the Yellow River in China.
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