Understanding Watershed

A watershed is the entire land area that drains into a single creek, river, lake or estuary. The boundary of a watershed is determined by the hills and valleys of the landscape.

Generally, ridgelines determine the shape and boundaries of a particular watershed. Precipitation falling on 1 side of a ridge flows to 1 watershed, while precipitation falling on the other side of a ridge flows to a different watershed. Every piece of land is part of a watershed.
Watershed Diagram
Types of Watersheds
Watersheds come in many different shapes and sizes. A river basin is generally a large watershed, whereas subwatersheds or drainage areas are smaller delineations determined by the stream of interest. These terms are frequently used interchangeably. Watersheds are named for the streams that they drain into. The U.S. Geological Survey in cooperation with the U.S. Board on Geographic Names maintains a database of stream names and is responsible for reviewing/approving requests for name additions and modifications.

Harford County contains 4 major river basins - the Bush River Basin, the Gunpowder River Basin, the Lower Susquehanna River Basin, and the Upper Western Shore Basin, which all drain to the Chesapeake Bay Watershed. These larger watersheds are made up of many smaller watersheds. For example, the Bush River Basin is comprised of the Otter Point Creek, Bush Creek, and Church Creek Subbasins.

Everyone lives in a watershed. How we use the land (farms, houses, businesses, industry), what covers the land (lawns, crops, forests, pavement), and our land use habits (use of pesticides and fertilizers, disposal of toxic wastes, garbage disposal, clean up of animal wastes) all affect water quality within the watershed. Precipitation falling within a watershed runs off the land and into a water body, carrying with it various pollutants including nutrients and sediments.