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Introduction to Watersheds

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.

Shaded map showing the outline of two watersheds.

The yellow lines represent the boundaries of neighboring watersheds. Note how the boundaries follow areas of high elevation.

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Montgomery County and the Chesapeake Bay

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.

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How Do Watersheds Affect Your Quality of Life?

Clean watersheds offer you (and the local environment) many benefits:

  • Recreational opportunities like boating, swimming, picnicking, and wading.
  • Habitat for wildlife and fish. (Good water quality is important for both fish and their food web.)
  • Increased value for real estate. (Beautiful, clean water in streams and lakes is an amenity that people pay a premium to be near.)
  • Lower-cost drinking water (because the water doesn't require expensive treatment before it's piped to your home).
  • Aesthetically pleasing surroundings. (Clean waterways offer beauty in the landscape.)
  • An escape from urban development. (Waterfronts are peaceful places that people enjoy.)
  • Better public health and safety. (Polluted water is a health hazard.)
  • Reduced tax burdens. (Protecting the watershed reduces the tax burden now and into the future because taxpayers pay less to clean up and protect the environment.)

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.

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How Do You Affect Your Watershed?

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.

Effect Example

Pollutant-laden Runoff

Rainfall is a major source of water in watersheds. As it flows over urban areas, it's carried by storm drains off streets and parking lots, directly into drains and creeks and eventually into streams. This runoff, known as stormwater, carries with it everything we leave on the landscape:
  • Trash and litter from urban areas
  • Sediment and dirt
  • Leaking automotive fluids and oil
  • Pet waste left on the ground
  • Excess fertilizer and pesticides from lawns and gardens
  • Leaves and grass clippings
  • Dust from roofs and roads

Learn how you can help stop stormwater pollution.

Photo of a parking lot with storm drains.

Polluted runoff runs off impervious surfaces, such as parking lots.

Illegal Dumping

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.

PPhoto of a stream with trash.

Illegal dumping pollutes our streams.

Erosive Streamflows Caused by Impervious Urban Areas

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.

Photo of a man standing next to an eroded stream bank.

See how erosive stormflows damage local streams.

Septic Systems

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.

 

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Last edited: 8/26/2010