The Lake Champlain Basin or watershed is the entire drainage area for Lake Champlain. Rain, snow, sleet or any precipitation that falls on the watershed will eventually reach the Lake. Watersheds are defined by bodies of water. Some watersheds can be very small, defining minor tributaries, or very large, encompassing vast river systems. Because of this, larger watersheds can contain many smaller watersheds. Lake Champlain's watershed is made up of many smaller watersheds which are defined by the numerous rivers and tributaries which flow to Lake Champlain.

Scientists classify watersheds into designations called hydrological units. Each unit is uniquely identified by a series of numbers. This allows smaller watersheds to be identified within the larger watersheds. The larger the hydrological unit number, the smaller the watershed. For example, an eight digit hydrological unit can be comprised of a number of eleven digit units, which in turn are defined by any number of fourteen digit watersheds. The Watersheds as Hydrological Units Map [333 KB] illustrates the Lake Champlain Basin's eight and fourteen digit watershed boundaries.

Classifying watersheds into hydrological units is useful for watershed planning and management. Watersheds can be reorganized into more natural groupings, which are unconstrained by political boundaries. The Lake Champlain Basin Program commonly uses several groupings of watersheds in its research. The eight digit hydrological unit is used in modeling the influence of major river systems, particularly in terms of land use and phosphorus loads. Eleven and fourteen digit watersheds are used for research which benefits from a more detailed examination of the landscape.

Watersheds can also be grouped according to Lake Champlain's lake segments. The Watersheds by Lake Segments Map [608 KB] shows this grouping. Unlike many other lakes which are shaped like bowls and tend to be more evenly mixed, Lake Champlain is made up of distinct areas or lake segments, each with different physical and chemical properties. Watersheds are grouped with reference to the lake segment they drain, allowing researchers to loosely correlate the watersheds' characteristics with the physical and chemical properties of the particular lake segment.

• Surf Your Watershed - US EPA
• Watersheds Pages (LCBP)