The start of a river is called its source. Large portions of the world's largest rivers begin in hollows in the land. Water drips in from the surrounding soil to allow the formation of a tiny flow of water called a seep. Don't underestimate such a seep, because even huge rivers such as the Nile in Egypt start from small sources like this.

Other rivers start from a marsh or a lake. Some rivers begin their journey as winter snow high up in the mountains. As the snow begins to melt, streams of water begin pouring down by the mountainsides. In the beginning, the water filters into the ground. The pores in the ground eventually fill up and close under the impact of the raindrops in spring. As the land becomes soaked in water, excess rain flow from the side of the mountains as surface runoff. The mountain-stream water runs freely without any major riverbeds at first. The water causes erosion as it flows, tearing away matter from the mountainside and carrying it into the valleys. Various streams of run-off water join together to form creeks which eventually merge to form large rivers.

Photo: Debbie Rach