# Patapsco River

The Patapsco River (/pəˈtæpˌskoʊ/ pə-TAP-skoh ) mainstem is a 39-mile (63 km) 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".

## History

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. 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.
The first land record regarding Parr's Springs, the source of the South Branch, 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. Parr's Spring was dug to form a 1.75 acres (7,100 m$^2$) pond in the 1950s, filled by seven spring heads that form the headwaters of the South Branch of the Patapsco River.
Beginning in the 1770s, the Patapsco River became the center of Maryland industrialization. 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. 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.
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.
Bloede's Dam, a hydroelectric dam built in 1906, was on the Patapsco River within Patapsco Valley State 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. 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. Dam demolition began on September 12, 2018, opening the fishery and creating a rocky rapid for kayaking. Two dams upstream of Bloede's Dam, Simkins and Union, were removed in 2010. The removal of Bloede's Dam leaves Daniels Dam, 9 miles (14 km) upstream, as the last remaining dam along the mainstem Patapsco River.
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.

## Course

The 19.4-mile-long (31.2 km) South Branch rises 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. The South Branch Patapsco River traces the southern boundary of Carroll County and the northern boundary of Howard County.
The North Branch flows 20.9 miles (33.6 km) 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.
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. Through most of its length, the Patapsco is a minor river flowing mostly through a narrow valley. 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.
The last 10 miles (16 km), form a large tidal estuary inlet of Chesapeake Bay. Two lobes of the harbor deviate from the "mainstem" harbor: the Middle Branch Patapsco River, into which Gwynns Falls; and the Northwest Branch Patapsco River, into which Jones Falls flows. The inner part of this estuary provides the harbor of Baltimore. Thoms Cove is further down the main harbor. The Patapsco estuary is south of the Back River and north of the Magothy River.

## Tributaries

The Patapsco has a watershed (including the water surface) of 950 square miles (2,460 km$^2$).
* 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. 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.
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.

## 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. The Piney Run Reservoir on the South Branch of the Patapsco is polluted by excess levels of phosphorus and sediment.
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.

## Recreation

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.

## Crossings

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 |
| | Spring Garden Swing Bridge | Western Maryland Railway | Baltimore | 1904 | Crosses Middle Branch only |
| | Ridgleys Cove interchange | I-95 I-395 | Baltimore | | Crosses Middle Branch only |
| | Light rail bridge | Baltimore Light RailLink | Baltimore | | Crosses Middle Branch only |
| | Hanover and Potee Street Bridges | MD 2 | Baltimore | 1973 | Hanover Street Bridge reconstructed in 2005 |
| | 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 |
| | 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 |
| | Hammonds Ferry Road bridge | Hammonds Ferry Road | Linthicum Lansdowne | 1961 | |
| | Baltimore Beltway bridge | I-695 | Linthicum Lansdowne | 1958 | Refurbished in 1982 |
| | Northeast Corridor bridge | Amtrak Northeast Corridor | Linthicum Halethorpe | | |
| | I-195 bridge | I-195 | Elkridge Halethorpe | 1988 | |
| Howard County – Baltimore County ||||||
| | I-895 bridge | I-895 | Elkridge Relay | 1973 | On/off ramp bridges flank US 1 bridge to north and south |
| | Patapsco River Bridge | US 1 | Elkridge Relay | 1915 | Concrete arch bridge refurbished in 1952 |
| | Thomas Viaduct | B&O Capital Subdivision | Elkridge Relay | 1835 | World's largest multiple arched bridge. Named after Philip E. Thomas. |
| | I-95 bridge | I-95 | Elkridge Relay | 1968 | |
| | 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. |
| | Main Street Bridge | MD 144 | Ellicott City Oella | 1914 | |
| | Baltimore National Pike Bridge | US 40 | Ellicott City Catonsville | 1936 | Reconstructed using original arches in 2014 |
| | I-70 bridge | I-70 | Ellicott City Catonsville | 1966 | |
| | 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 ||||||