A watershed is an area of land that drains to a common body of water, such as a nearby creek, stream, river or lake. Watersheds vary considerably in size. For example, when it rains, all the water from a small watershed may travel to a local creek. That creek will flow into a larger stream, like Mill Creek, which collects water from an even larger watershed. Mill Creek flows into the Kansas River, which then deposits water into the Missouri River.