The Basics
Keeping North Dakota�s lakes and streams clean demands more than dockside diligence. Even if you don�t live along the shores or banks, you may be contributing to the pollution of lakes and streams. Lakes and streams are larger than their shorelines. They�re part of a system called a watershed.

What is a watershed?
Water from rainfall or snowmelt that doesn�t evaporate or soak into the soil runs into ditches, streams, wetlands, or lakes. The land area from which the water drains is called a watershed.

Watersheds may vary in size. If water from a few acres drains into a little stream, those few acres are its watershed. This stream and others like it run into larger streams or lakes. Small watersheds make up larger ones. It�s easy to see how the watersheds of North Dakota�s lakes can have land areas many times larger than their lake surfaces.

A watershed is simply defined as, "an area of land that drains to a common point, usually a stream, river, lake or wetland".

For more on the basics click these:
Water and People
Water Cycle