Just as a city, county or state has boundaries, so does a watershed. We define a watershed as the land that contributes water to a given site. Think of this as a line that connects all of the highest points in an area – as illustrated in the animation at right. Precipitation falling inside this line is delivered to small streams or tributaries which join to form rivers. A watershed with its small tributary streams and larger river can be compared to a leaf with its sub-veins and main vein.

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