DEP Home : Water : Introduction to Watersheds
For questions about watersheds contact DEP:
Montgomery County sits right in the middle of the Chesapeake Bay watershed.
Clean water has many benefits.
A watershed is an area from which the water above and below the ground drains to a particular stream, river, lake, bay, or ocean.
The watershed boundary is defined by the dividing line of highest elevation surrounding a given stream or network of streams. Rainwater falling outside the boundary will flow into an adjacent watershed and another receiving water body.
The yellow lines represent the boundaries
of neighboring watersheds. Note how the boundaries follow
areas of high elevation.
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The relatively small watersheds within Montgomery County combine to form larger watersheds. For example, all the land that drains into Rock Creek makes up the Rock Creek watershed. This watershed is part of the Potomac River watershed because Rock Creek flows into the Potomac River. The same drainage area is also part of the larger Chesapeake Bay watershed because the Potomac River empties into the Chesapeake Bay.
Clean watersheds offer you (and the local environment) many benefits:
By protecting our watersheds and preventing pollution, we secure our quality of life and reduce the costs of government cleanup programs. Also, keeping our water clean helps protect the water supply for people and animals that live downstream, allowing them to experience the same benefits.
Everything you do on the land and in your yard and neighborhood directly affects the water quality of local streams. Many of the practices and devices you might take for granted—from fertilizing the lawn to operating a septic system—can affect water bodies.
Learn how you can help stop stormwater pollution.
Polluted runoff runs off impervious surfaces, such as parking lots.
Anything that is flushed or poured down a storm drain goes directly into local streams without being treated to remove the pollutants. Automotive fluids dumped down a storm drain are one unfortunate example. Dumping items like tires, lawn care debris, or large household appliances and old bicycles directly into a stream channel also affects the health and beauty of the stream.
Learn how to properly dispose of household waste.
Illegal dumping pollutes our streams.
In highly urban areas, many stream networks have been channeled into concrete pipes beneath the roads to clear the way for urban development. Runoff from urban surfaces like parking lots and streets flows at high velocities through these pipes. When the pipes eventually empty into streams, the runoff is fast-flowing and highly erosive. As a result, stream banks are destroyed, tree roots are exposed, and the stream's ability to function as a healthy aquatic ecosystem is damaged.
See how erosive stormflows damage local streams.
Septic systems can threaten surface waters and groundwater through the migration of pollutants into the waters beneath the septic systems. Even with proper siting and installation, various operational issues and a lack of regular pumping and maintenance can cause septic systems to malfunction.