Summary #
A watershed is the land area that drains to a single body of water. No matter where you live, you live in a watershed. Understanding watersheds — their boundaries, scales, and nested structure — is the starting point for all monitoring, assessment, and restoration work. Pennsylvania is divided into six major watersheds that drain into the Chesapeake Bay, Lake Erie, and the Ohio River.
What is a Watershed? #
No matter where you live, you live in a watershed.
A watershed is the land area that drains to a single body of water such as a stream, lake, wetland, or estuary. Hills or ridgelines often bound watersheds; interior valleys collect precipitation in streams, rivers, and wetlands. These physical boundaries define the movement of water and delineate the watershed. Watersheds — also known as catchments or basins — describe geography at many different scales: a few acres may drain to a small stream or wetland; a few large rivers may drain into an estuary where fresh and salt water mix; about 40 percent of the U.S. land area in the lower 48 states drains to the Mississippi River. Watersheds are “nested” — larger watersheds such as the Mississippi River basin encompass many smaller watersheds.
Source: EPA Office of Water, Protecting and Restoring America’s Watersheds, EPA-840-R-00-001. See also: River of Words: http://www.riverofwords.org/watershed.html
Pennsylvania’s Watersheds #
Pennsylvania is divided into six major watersheds: the Ohio, the Genesee, the Susquehanna, the Delaware, the Erie, and the Potomac. These drain large portions of the state into major waterways including the Chesapeake Bay, Lake Erie, and the Ohio River.
Each of these major watersheds contains thousands of smaller watersheds. As the size of the waterway decreases, so does the drainage area. When considering watershed rehabilitation, work at a manageable scale — 50,000 acres or less is a practical target.
See the PA Environmental Council’s treatment of watershed geography: http://www.watershedatlas.org/fs_indexwater.html
To find out what watershed you live in, start with: http://amrclearinghouse.org/Sub/WATERSHEDbasics/MappingYourWatershed.htm
Related Pages #
- Mapping Your Watershed
- Water Cycle
- Ground Water
- Watershed Assessment Hub (Watershed Tools — Watershed Assessment)
- Background Search (Watershed Tools — Watershed Assessment)
Source and Last Reviewed #
Source: EPA Office of Water, Protecting and Restoring America’s Watersheds, EPA-840-R-00-001.
Additional: http://www.riverofwords.org/watershed.html | http://www.watershedatlas.org/fs_indexwater.html
Last reviewed: 2026-03 | Links may require verification — originally published pre-2010.
Tags: monitoring, assessment, practitioner, volunteer, pa
