The source is the farthest point of the river stream from its estuary or its confluence with another river or stream. Rivers are usually fed by many tributaries. The farthest stream is called the headstream or headwater. They are usually cool waters because of shade and barely melted ice or rain. They may also be glacial headwaters. These are waters made by melting glaciers.
The source is where a river begins, and the mouth is where it joins the sea. The source of a river generally discharges water with less force leading to the formation of Interlocking spurs.