The Patapsco River mainstem is a 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", was named after the clay color, and 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 major path of commerce with only one ship listed as serving the northern branch, and four others operating around the mouth in 1723. The Patapsco River is referred to as The River of History as it is regarded as the center of Maryland’s Industrial Revolution beginning in the 1770s. Milling and manufacturing operations abounded along the river throughout the eighteenth and nineteenth centuries, generally relying on water power generated by multiple small dams. The nation’s first railroad, the Baltimore and Ohio Railroad's original main line was constructed in 1829 and ran west along the Patapsco Valley; and this route remains, though much altered. Many old railroad bridges were constructed in the valley, most notably the Thomas Viaduct, which is still intact, and the Patterson Viaduct, of which ruins remain. Flour mills and the hydropower dam, Bloede Dam, built in 1907, were formerly powered by the river. The valley is prone to periodic flooding. Modern floods include the 1868 flood that washed away 14 houses and killed 39 people around Ellicott City. A 1923 flood topped bridges while in 1952, an wall of water swept the shops of Ellicott City. A 1956 flood inflicted heavy damage at the Bartigis Brothers plant. In 1972, as a result of rainfall from the remnants of Hurricane Agnes, Ellicott City and the Old Main Line sustained serious damage. The July 2016 Maryland flood ravaged Main Street leaving two dead, followed just two years later by a flash flood on May 27, 2018 that took the life of one 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, while