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Patapsco River

Coordinates: 39°10′25″N 76°26′36″W / 39.1737202°N 76.4432935°W / 39.1737202; -76.4432935
From Wikipedia, the free encyclopedia

Patapsco River
The River of History
Patapsco River Watershed
Native namePotapskut (Algonquian languages)
CountryUnited States
RegionBaltimore metropolitan area, Patapsco Valley
CitiesBaltimore, Elkridge, Ellicott City
Physical characteristics
 • locationMarriottsville
 • coordinates39°20′59″N 76°52′56″W / 39.3498272°N 76.8821987°W / 39.3498272; -76.8821987
 • elevation260 ft (79 m)
MouthChesapeake Bay
 • location
 • coordinates
39°10′25″N 76°26′36″W / 39.1737202°N 76.4432935°W / 39.1737202; -76.4432935
 • elevation
0 ft (0 m)
Length63 км
Basin size950 sq mi (2,460 km2)
Basin features
 • leftNorth Branch
 • rightSouth Branch
The Inner Harbor viewed from the Baltimore Aquarium
Liberty Reservoir
Volunteers at a community cleanup of Herbert Run, a tributary of the Patapsco River running through Arbutus, Maryland

The Patapsco River (/pəˈtæpˌsk/ pə-TAP-skoh ) mainstem is a 39-mile (63 km)[1] river in central Maryland that flows into the Chesapeake Bay. The river's tidal portion forms the harbor for the city of Baltimore. With its South Branch, the Patapsco forms the northern border of Howard County, Maryland. The name "Patapsco" is derived from the Algonquian pota-psk-ut, which translates to "backwater" or "tide covered with froth".[2]



Captain John Smith was the first European to explore the river, noting it on his 1612 map as the Bolus River. The "Red river", named after the clay color, is considered the "old Bolus", as other branches were also labeled Bolus on maps.[3] As the river was not navigable beyond Elkridge, it was not a significant path of commerce; in 1723, only one ship was listed as serving the northern branch, and four others operating around the mouth.[4]

Beginning in the 1770s, the Patapsco River became the center of Maryland industrialization.[5] Milling and manufacturing operations abounded along the river throughout the eighteenth and nineteenth centuries, generally powered by small dams. The Baltimore and Ohio Railroad's original main line was constructed in 1829 west along the Patapsco Valley; the nation's first railroad, the route remains, though much altered. Many railroad bridges were built in the valley, including the Thomas Viaduct, which is still in use, and the Patterson Viaduct, now in ruins. The 1907 hydropower Bloede's Dam powered flour mills.

An 1868 flood washed away 14 houses and killed 39 people around Ellicott City. A 1923 flood topped bridges. In 1952, an 8 ft (2.4 m) wall of water swept the shops of Ellicott City. A 1956 flood severely damaged the Bartigis Brothers plant.[6] In 1972, rainfall from the remnants of Hurricane Agnes damaged Ellicott City and the Old Main Line. Two died in the July 2016 Maryland flood ravaged Main Street, followed two years later by a May 2018 Maryland flood that took the life of a rescuer.[7]

The mouth of the Patapsco River forms Baltimore Harbor, the site of the Battle of Baltimore during the War of 1812. This is where Francis Scott Key, aboard the British HMS Tonnant, wrote "The Star-Spangled Banner", a poem later set to music as the national anthem of the United States. Today, a red, white, and blue buoy marks where the ship was anchored.

In the early hours of March 26, 2024, the 1.6-mile-long (2.6 km) Francis Scott Key Bridge, which carried Interstate 695 over the Patapsco River, was struck by a container ship and partially collapsed into the river.[8]





The Patapsco has a watershed (including the water surface) of 950 square miles (2,460 km2).[9] Through most of its length, the Patapsco is a minor river flowing mostly through a narrow valley. The last 10 miles (16 km), however, form a large tidal estuary inlet of Chesapeake Bay. The inner part of this estuary provides the harbor of Baltimore, composed of the Northwest Harbor and the Middle Branch, including Thoms Cove. (See Baltimore Inner Harbor.) The Patapsco estuary is south of the Back River and north of the Magothy River. The Patapsco River forms the harbor as it empties into the Chesapeake Bay. Besides Baltimore, the river also flows through Ellicott City (the county seat of Howard County) and Elkridge.

The Patapsco River mainstem begins at the confluence of the North and South Branches, near Marriottsville, about 15 miles (24 km) west of downtown Baltimore. The 19.4-mile-long (31.2 km)[1] South Branch rises further west at Parr's Spring, where Howard County, Carroll, Frederick, and Montgomery counties meet. The latter begins at elevation 780 feet (240 m) on Parr's Ridge, just south of Interstate 70 and east of Ridge Road (Highway 27), 2 miles (3 km) south of Mount Airy, Maryland.[1] The South Branch Patapsco River traces the southern boundary of Carroll County and the northern boundary of Howard County. The first land record regarding Parr's Springs dates from 1744, when John Parr laid out a 200 acres (81 ha) tract he called Parr's Range. During the Civil War, Parr's Spring was a stop for the Army of the Potomac's Brig. Gen. David M. Gregg's cavalry, on June 29, 1863, while en route to Gettysburg, Pennsylvania.[10] Parr's Spring was dug to form a 1.75 acres (7,100 m2) pond in the 1950s, filled by seven spring heads that form the headwaters of the South Branch of the Patapsco River.[11]

The North Branch flows 20.9 miles (33.6 km)[1] southward from its origins in Carroll County. Liberty Dam and its reservoir on the North Branch are major components of the Baltimore City water system.[12]

Patapsco Valley State Park extends along 32 miles (51 km) of the Patapsco and its branches, encompassing 14,000 acres (5,700 ha) in five areas. The river cuts a gorge 100 to 200 feet (35–70 m) deep within the park, with rocky cliffs and tributary waterfalls. Bloede's Dam, a hydroelectric dam built in 1906, was on the Patapsco River within the park, a nearly complete barrier to anadromous fish passage. Although a fish ladder was installed in 1992, it blocked five of six native fish species trying to run upstream to spawn.[13] Efforts to remove Bloede's Dam began in the 1980s when nine drowning deaths occurred, and also to restore fish passage to a large portion of the Patapsco River watershed.[14][15] Dam demolition began on September 12, 2018, opening the fishery and creating a rocky rapid for kayaking.[16] Two dams upstream of Bloede's Dam, Simkins and Union, were removed in 2010.[17][9] The removal of Bloede's Dam leaves Daniels Dam, 9 miles (14 km) upstream, as the last remaining dam along the mainstem Patapsco River.[13]


  • Deep Run (Carroll County)
  • Board Run (Baltimore County)
  • Roaring Run (Carroll County)
  • Liberty Reservoir (Carroll/Baltimore Counties)
  • Piney Run (Carroll County)
  • Keysers Run (Baltimore County)
  • Beaver Run (Carroll County)
  • Norris Run (Baltimore County)
  • Timber Run (Baltimore County)
  • Middle Run (Carroll County)
  • Morgan Run (Carroll County)
  • Locust Run (Baltimore County)
  • Snowdens Run (Carroll County)
  • Falls Run (Baltimore County)
  • South Branch Patapsco River
  • Davis Branch (Howard County)
  • Brice Run (Baltimore County)
  • Bens Run (Baltimore County)
  • Cedar Branch (Baltimore County)
  • Miller Run (Baltimore County)
  • Sucker Branch (Howard County)
  • Tiber River (Howard County)
  • Cooper Branch (Baltimore County)
  • Bonnie Branch (Howard County)
  • Sawmill Branch (Baltimore County)
  • Cascade Falls (Howard County)
  • Soapstone Branch (Baltimore County)
  • Rockburn Branch (Howard County)
  • Deep Run (Howard/Anne Arundel County)
  • Stony Run (Anne Arundel County)
  • Herbert Run (Baltimore County)
  • Holly Creek (Anne Arundel County)
  • Middle Branch to Gwynns Falls (Baltimore City)
  • Northwest Harbor to Jones Falls (Baltimore City)
  • Colgate Creek (Baltimore City)
  • Curtis Creek (Baltimore City)
  • Bear Creek (Baltimore County)
  • Cox Creek (Anne Arundel County)
  • Stoney Creek (Anne Arundel County)
  • Rock Creek (Anne Arundel County)
  • Old Road Bay (Baltimore County)
  • Bodkin Creek (Anne Arundel County)

Ecology and conservation


The removal of Bloede's Dam in September 2018, opened up 65 miles (105 km) of the Patapsco River watershed, which will potentially restore spawning runs of at least six species of native anadromous fish: alewife (Alosa pseudoharengus), blueback herring (Alosa aestivalis), American shad (Alosa sapidissima), hickory shad (Alosa mediocris), striped bass (Morone saxatilis), sea lamprey (Petromyzon marinus), as only one species, sea lamprey, were found using the Bloede's Dam fish ladder in 2012.[13] One catadromous species would likely also benefit, the American eel (Anguilla rostrata), a fish species that lives in freshwater and migrates to the ocean to breed. The Bloede's Dam removal project was led by American Rivers and the Maryland Department of Natural Resources.[13]

Now that Bloede's Dam has been removed, removal of Daniels Dam upstream on the mainstem Patapsco River would open to anadromous fishes the remaining 6.5 miles (10.5 km) of Patapsco River mainstem, the entire 19.4 miles (31.2 km) length of the South Branch Patapsco River, 3.5 miles (5.6 km) of the North Branch Patapsco River up to the Liberty Dam, and many of these rivers' tributaries.[1]

Water quality


The eastern portion of the Patapsco River is in a highly urbanized area and is subject to extensive stormwater runoff and other forms of water pollution. The Maryland Department of the Environment has identified the Lower North Branch as containing high levels of heavy metals (chromium, arsenic, cadmium, copper, mercury, nickel, lead, selenium, and zinc), as well as phosphorus, fecal coliform bacteria, and PCBs.[18] The Piney Run Reservoir on the South Branch of the Patapsco is polluted by excess levels of phosphorus and sediment.[19]

Environmental nonprofit organizations, such as The Friends of Patapsco Valley & Heritage Greenway, Inc. (PHG), lead clean-up efforts by the residents of surrounding communities. From 2006 to 2012, PHG volunteers participated in 183 stream clean-ups, removing 264 tons of trash from the streams of the Patapsco Valley watershed.[20]



Recreational swimming is possible in areas of the Patapsco River, sometimes involving rope swings, inner tubing, and wading. The river also serves as a venue for rafting. The Patapsco is also great for fishing. The MD DNR stocks parts of Patapsco State Park in the early spring and offers some pretty decent trout fishing. The Northern Snakehead has also made the Patapsco their home. They can be found from historic Ellicott City to the harbor.



This is a list of all crossings of the main stem of the Patapsco River, as well as its two downstream short branches, the Middle Branch and Northwest Branch. Listings start downstream and continue upstream to the sources of the rivers.

Image Crossing Carries Location Opened Notes
Anne Arundel County – Baltimore County
Francis Scott Key Bridge I-695 Baltimore 1977–2024 Collapsed after being struck by a container ship on March 26, 2024
Baltimore Harbor Tunnel I-895 Baltimore 1957 $4.00 toll
Fort McHenry Tunnel I-95 Baltimore 1985 Crosses Northwest Branch only; $4.00 toll
Hanover Bridge MD 2 Baltimore Crosses Middle Branch only
Ridgleys Cove interchange I-95


Baltimore Crosses Middle Branch only
Hanover and Potee Street Bridges MD 2 Baltimore 1973 Hanover Street Bridge reconstructed in 2005[21]
Curtis Bay Branch Railroad bridge B&O Curtis Bay Branch Baltimore
Patapsco Avenue bridge Patapsco Avenue Brooklyn, Baltimore 1961
I-895 bridge near South West Area Park I-895 Baltimore Highlands 1958 Refurbished in 2019[22]
Central Light Rail bridge Baltimore Light Rail Baltimore Highlands 1908 Previously used for the Baltimore and Annapolis Railroad
Old Annapolis Road bridge MD 648 Baltimore Highlands
BW Parkway bridge MD 295 Baltimore Highlands 1948 Refurbished in 1985[23]
Hammonds Ferry Road bridge Hammonds Ferry Road Linthicum
Baltimore Beltway bridge I-695 Linthicum
1958 Refurbished in 1982[24]
Northeast Corridor bridge Amtrak Northeast Corridor Linthicum
I-195 bridge I-195 Elkridge
Howard County – Baltimore County
I-895 bridge I-895 Elkridge
1973 On/off ramp bridges flank US 1 bridge to north and south
Patapsco River Bridge US 1 Elkridge
1915 Concrete arch bridge refurbished in 1952[25]
Thomas Viaduct B&O Capital Subdivision Elkridge
1835 World's largest multiple arched bridge. Named after Philip E. Thomas.[26]
I-95 bridge I-95 Elkridge
Gun Road bridge Gun Road Relay Patapsco Valley State Park access only
Patapsco Swinging Bridge Swinging Bridge Trail Ilchester 2006 Pedestrian bridge connecting River Road to Grist Mill Trail
Patterson Viaduct Grist Mill Trail Ilchester 2006 Former rail bridge opened 1829, destroyed 1868, and rebuilt 1869; new footbridge built on abutments of prior rail bridge
Ilchester Bridge Old Main Line Subdivision Ilchester 1903
Ilchester Road bridge Ilchester Road Ilchester Known as Heartbeat Bridge in local folklore.[27]
Main Street Bridge MD 144 Ellicott City
Baltimore National Pike Bridge US 40 Ellicott City
1936 Reconstructed using original arches in 2014[28]
I-70 bridge I-70 Ellicott City
Hollifield Bridge Old Frederick Road Daniels 1934
Daniels bridge Old Main Line Subdivision Daniels
Eureka bridge Old Main Line Subdivision Mt. Airy
MD 125 bridge MD 125 Woodstock 1981
Patapsco River North Branch-South Branch confluence

See also



  1. ^ a b c d e "The National Map - Advanced Viewer". apps.nationalmap.gov. Retrieved April 5, 2023.
  2. ^ "Ghosts of industrial heyday still haunt Baltimore's harbor, creeks". Chesapeake Bay Journal. Retrieved September 8, 2012.
  3. ^ John Thomas Scharf. The Chronicles of Baltimore: Being a Complete History of Baltimore Town. p. 8.
  4. ^ John Thomas Scharf. The Chronicles of Baltimore: Being a Complete History of Baltimore Town. p. 18.
  5. ^ Paul J. Travers (2016). The Patapsco: Baltimore's River of History. Schiffer Publishing Limited. p. 220. ISBN 978-0-87033-644-7. Retrieved September 14, 2018.
  6. ^ "The Patapsco River Creator-Destroyer". The Times (Ellicott City). March 31, 1965.
  7. ^ "'Devastating, dangerous' | Ellicott City's Main Street hit with flooding again". www.11alive.com.
  8. ^ "Baltimore bridge collapses after powerless cargo ship rams into support column; 6 presumed dead". AP News. March 26, 2024. Retrieved March 26, 2024.
  9. ^ a b Yantao Cui; Mathias J. Collins; Mary Andrews; Graham C. Boardman; John K. Wooster; Marty Melchior; Serena McClain (2018). "Comparing 1-D sediment transport modeling with field observations: Simkins Dam removal case study". International Journal of River Basin Management. 17 (2): 1–13. doi:10.1080/15715124.2018.1508024. S2CID 133928458.
  10. ^ Frederic Shriver Klein (2000). Just South of Gettysburg: Carroll County, Maryland in the Civil War: Personal Accounts and Descriptions of a Maryland Border County. Historical Society of Carroll County. p. 247.
  11. ^ Sheridan Lyons (May 15, 2000). "Beneath the pier, 4 counties meet". The Baltimore Sun. Retrieved September 16, 2018.
  12. ^ Baltimore County Department of Environmental Protection and Resource Management. Towson, MD. "Patapsco River Watershed." 2009-07-13.
  13. ^ a b c d William Harbold; Scott Stranko; Jay Kilian; Matt Ashton; Patrick Graves (May 1, 2013). Patapsco River Dam Removal Study: Assessing Changes in American Eel Distribution and Aquatic Communities – Final Report (PDF) (Report). Maryland Department of Natural Resources. Retrieved September 4, 2018.
  14. ^ Rachael Pacella (March 23, 2016). "Bids set to go out for removal of Bloede Dam at Patapsco Valley State Park". The Baltimore Sun.
  15. ^ "Man, 18, drowns near dam". The Baltimore Sun. May 22, 1982. p. C2.
  16. ^ "Bloede Dam". dnr.maryland.gov. Retrieved March 29, 2024.
  17. ^ Scott Dance (September 5, 2018). "After a century on the Patapsco River, Bloede Dam's removal set to begin with a blast". The Baltimore Sun. Retrieved September 5, 2018.
  18. ^ "TMDLs and Water Quality Plans for the Lower North Branch Patapsco River". Baltimore, MD: Maryland Department of the Environment (MDE). Retrieved March 12, 2022.
  19. ^ "TMDLs and Water Quality Plans for the South Branch Patapsco River". MDE. Retrieved March 12, 2022.
  20. ^ "Protecting the Valley". Friends of Patapsco Valley & Heritage Greenway, Inc. Retrieved May 24, 2012.
  21. ^ "Potee Street Bridge". www.google.com. Retrieved March 29, 2024.
  22. ^ "I-895 bridge". www.google.com. Retrieved March 29, 2024.
  23. ^ "BW Parkway bridge, MD 295". www.google.com. Retrieved March 29, 2024.
  24. ^ "Baltimore Beltway bridge". www.google.com. Retrieved March 29, 2024.
  25. ^ "Patapsco River Bridge". bridgehunter.com.
  26. ^ "Thomas Viaduct". dnr.maryland.gov. Retrieved March 29, 2024.
  27. ^ "Haunted Ellicott City". Historic Ellicott City, MD. Archived from the original on August 28, 2006. Retrieved March 26, 2024.
  28. ^ "US40 Patapsco River Bridge". bridgehunter.com.