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Protecting the Valley

Overall Patapsco Watershed Assessment


The 375,000 acres of the Patapsco River Watershed are located within Anne Arundel, Baltimore, Carroll, and Howard counties, as well as Baltimore City, Maryland. The South branch of the Patapsco River (and thus the main stem of the Patapsco) flows about 35 miles from Parr's Spring in Carroll County to Baltimore City. The North branch of the Patapsco is formed at the confluence of the East and West branches, flows through Liberty Reservoir and then joins the South branch near Sykesville. The Patapsco's headwaters consist of springs and seeps which converge to form high gradient streams flowing through steep ravines. As these join, the streams become a river, with a slightly lower gradient and larger flows. From Sykesville, the river's floodplain continues to widen until it reaches a significant restriction in the vicinity of Oella/Ellicott City. From there, the floodplain again begins to widen until it flows into the Middle Branch of the Baltimore Harbor. The river at this point becomes tidal and enters the Chesapeake Bay.  A watershed map can be found at http://mddnr.chesapeakebay.net/wsprofiles/surf/prof/patback_profmap.html

Land Use

The Patapsco River watershed's land use is diverse. The watershed consists of forested areas, rural areas, productive farms, as well as suburban, urban and industrial areas. It is experiencing significant urban development at this time. One of the largest remaining forested areas in the watershed is the Patapsco Valley State Park which is a nearly contiguous forest buffer from Carroll County to Baltimore City.

Water Quality

Water quality within the Patapsco watershed has had a checkered past. Various types of monitoring have been conducted over the past three decades. The most recent efforts have been using macroinvertebrates as indicators. Certain sub-watersheds within the Patapsco are categorized based on Maryland Biological Stream Survey (MBSS) standards. Overall, there is a sense that with the elimination of various industries along the River and the increased availability of a public sewer system, that water quality has improved over the past 100 years. Current water quality problems appear to be from urbanization. Our present day challenge is increased impervious surfaces causing high rates of storm water runoff, in turn leading to higher sediment and nutrient loads. Details on water quality trends can be found at http://mddnr.chesapeakebay.net/eyesonthebay/tributary_health.cfm

Air Quality

The Patapsco watershed benefits from generally cleaner air now than its recent industrial past. The extensive forest cover undoubtedly serves as a significant producer of oxygen in an area which still has major producers of carbon dioxide (automobiles, power plants, manufacturers, etc). The trees may also help remove a variety of other pollutants from the air.

Endangered Species

The State of Maryland maintains a listing of all the plant and animal endangered species. Endangered plants and animals specific to the Patapsco watershed:

Patapsco Valley:

Scientific Name          Common Name      State Status

Dirca palustris               Leatherwood            Threatened
Matteucia struthiopteris  Ostrich Fern             Rare
Polygala senega            Seneca Snakeroot    Threatened

Soldiers Delight Natural Environmental Area:

Common Name

Sandplain Gerardia
Serpentine Aster
Fringed Gentian

Invasive Plants

Numerous invasive plants occur within the watershed such as Wavyleaf Basketgrass, Porcelainberry, Asiatic Bittersweet, English Ivy, Japanese Honeysuckle, Mile-a-minute, Bamboo, Garlic Mustard, etc. A recent addition (in 2007) is Wavyleaf Basketgrass which is spreading rapidly throughout Patapsco State Park areas despite a concerted effort to eradicate it (see http://dnr.maryland.gov/wildlife/plants_wildlife/wlbg/index.asp).


Noise levels within the watershed are no longer associated with the steady rhythm of the mills which used to dot the river banks. There are places within the watershed where you can get away from the hustle and bustle associated with a watershed located next to a large metropolitan area. As the urbanization of the watershed occurs, noise levels will continue to increase and become more prevalent. Aircraft flying over the watershed are a source of additional noise - particularly in the lower portion of the watershed near the BWI Airport.


© 2013 — Patapsco Heritage Greenway