Darby Creek is a tributary of the Delaware River in Chester County, Delaware County, and Philadelphia County, in Pennsylvania, in the United States. It is approximately 26 miles long. The watershed of the creek has an area of 77.2 square miles . It has twelve named direct tributaries, including Cobbs Creek, Little Darby Creek, Ithan Creek, and Muckinipattis Creek. The creek has a low level of water quality for most of its length. A reach of it is considered to be impaired by habitat modification, siltation, and flow variability stemming from urban runoff and storm sewers. The creek is slightly alkaline.
Darby Creek flows through a narrow valley in its upper reaches and a tidal flat in its lower reaches. The creek is in the Piedmont Uplands and Atlantic Coastal Plain physiographic provinces. Major rock formations in the watershed include the Wissahickon Formation. Three small dams historically existed on the creek, but were removed in 2012. The watershed of the creek is largely developed, with roughly half a million people inhabiting it. Most of the watershed is in Delaware County, but some parts are in Chester County, Philadelphia County, and Montgomery County. The watershed is part of the Lower Delaware drainage basin.
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