The place where a river begins is called its source. River sources are also called headwaters.

Rivers often get their water from many tributaries, or smaller streams, that join together. The tributary that started the farthest distance from the river's end would be considered the source, or headwaters.

Many rivers, including the Rhone in Western Europe, begin as streams in mountains or hills. As ice and snow melt, streams begin to flow downward from high mountains and the bases of glaciers.

When a glacier is a river's source, the river has glacial headwaters. The Ganges River has glacial headwaters. The source of the Ganges, in India and Bangladesh, is the Gangotri Glacier in the Himalayas of northern India.

Springs are the sources of some rivers. A spring is a place where water in the Earth, called groundwater, flows to the surface naturally. A spring forms when an aquifer, or natural underground reservoir, fills with groundwater and overflows. The spring of the Breg River, in Germany's Black Forest, is the source of the Danube.

Lakes with outflowing streams can become the headwaters of rivers, but only if they do not have streams that flow into them. (The inflowing stream—not the lake—would be a source of the river.) The Mississippi River, the largest river in North America, starts as a stream from Lake Itasca, a glacial lake in the U.S. state of Minnesota.