What is a watershed?

We all live, work, and play in a watershed. But what is a watershed? A watershed is an area from which the water above- and below-ground drains to a particular stream, river, lake, bay or ocean. Watersheds come in many shapes and sizes, and cross county, state, and national boundaries. Everyone lives in a watershed with a name and drainage boundaries. See below:

Map of Montgomery County Watersheds

A watershed is an area from which the water above- and below-ground drains to a particular stream, river, lake, bay, or ocean. Watersheds may be a few acres or many thousands of acres. Smaller watersheds combine to make up larger watersheds, creating a series of watersheds, known as a drainage basin, which may encompass several states. For example, all the land that drains into Rock Creek makes up the Rock Creek watershed. This land is also part of the Potomac River watershed, since Rock Creek flows into the Potomac River. This same drainage area is also part of the larger Chesapeake Bay watershed, because the Potomac River empties into the Chesapeake Bay. The Chesapeake Bay drains 64,000 square miles from six states and the District of Columbia.

In addition to streams, rivers, lakes, and other surface waters, watersheds include all the water that soaks into the ground and becomes part of the groundwater. Groundwater fills the spaces between rocks and soil particles underground, the same way that water fills a sponge. Groundwater slowly seeps into surface waters, including rivers, lakes, streams, and bays. This groundwater supply to streams is called baseflow. Contaminants, such as fertilizers and pesticides, can leach into the groundwater and, eventually, into the surface waters of a watershed.

What happens on the surrounding land in the smaller watersheds, whether good or bad, affects the larger watersheds downstream. Watersheds enhance our quality of life in Montgomery County.

Watersheds are:

places to play...
alive with wildlife -- birds, reptiles, amphibians, insects,
fish, and mammals ...
gifts of nature, places to relax...
sources of drinking water...
nature's boundaries.

For more information on watershed terms, visit our Watershed Glossary