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What is a watershed?
 How big is the Bay?

A watershed is the land area drained by a multitude of streams that flow downhill into a major river or lake or estuary.  Watersheds are also called drainage basins. Depending upon where you are in a network of streams draining the landscape (e.g., near the top in the headwaters or at the bottom on the shore of Chesapeake Bay), a watershed can be small (draining only a few acres), or very large (draining thousands of square miles).

watershedAnother way to think about a watershed is to imagine a large funnel open to the sky.  The funnel is analogous to a watershed, call it Watershed A.  Any rain, sleet or snow that falls inside the rim of this funnel belongs to Watershed A.  The rim of the funnel is analogous to a watershed boundary.  Hence, any rain or sleet or snow that falls outside the rim of this funnel belongs to adjacent watersheds. On the landscape, boundaries between watersheds are usually determined by elevation.

Map of targeted Maryland watersheds The Chesapeake Bay is the largest estuary in the United States. It is about 200 miles long. At the Bay Bridge near Annapolis, it is only 4 miles across, but it is 30 miles across at the widest point near the mouth of the Potomac River. The Bay watershed drains 64,000 square miles of land in six states- Maryland, Virginia, Delaware, Pennsylvania, West Virginia and New York and Washington, D.C. To give some idea of the size, the Bay watershed is about 5 times bigger than state of Maryland and 30 times larger than Delaware, yet it is only one-fourth the size of Texas!

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- Ron Klauda, Director
Monitoring & Nontidal Assessment
Maryland Department of Natural Resources

 For more information:
 Surf Your Watershed

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