The lower Darby Creek area was deemed a Superfund site by the U.S. Environmental Protection Agency (EPA) due to contamination with dangerous chemicals from two landfills.

As it continues downstream alongside the highway, it crosses Pennsylvania Route 3 and receives the tributary Longford Run from the left.

Further downstream, the creek's valley becomes much steeper and narrower and it makes several meanders as it passes by Clifton Heights and Landsowne before flowing along the border between Aldan and Yeadon.

The creek then flows south-southeast for a few miles, leaving its valley and passing Darby, Collingdale, Sharon Hill, and Colwyn as it crosses US Route 13.

[2] The creek turns south and enters the John Heinz National Wildlife Refuge 4.5 miles upstream from its mouth.

The causes of the impairment are habitat modification, siltation, and flow variability stemming from urban runoff and storm sewers.

[9] The valley of Darby Creek is considerably narrower in its upper reaches, but widens out as it approaches the Delaware River.

[10] Mica slate is present in Marple Township and was manufactured to form "Darby Creek scythe stones" in the 1860s.

[9] A large undeveloped tract of land owned by the Delaware County Industrial Development Authority is located at the mouth of the creek.

In 1643, Swedish colonists led by Johan Printz established New Sweden near the confluence of Darby Creek and the Delaware River.

In 1664, the Dutch surrendered the Darby Creek drainage basin to the English, who began settling the area after William Penn was issued a charter in 1681.

[11] The English settlers were attracted to the Darby Creek watershed due to the proximity to trading routes and productive landscape.

The Pennsylvania legislature passed an act in 1788 that mandated a maintenance of the dikes and the mowing of plants such as elderberries and pokeweed three times a year.

The dikes along the southern end of the creek were repaired by a joint force of the Works Progress Administration, the Pennsylvania legislature, and Delaware County.

The automobile replaced railroads as the dominant form of transportation, and it allowed workers to live farther from their places of employment.

[19] The Tinicum Wildlife Preserve was established in 1955 after the Gulf Oil Corporation donated a diked impoundment on the creek to the City of Philadelphia.

[14] They were demolished in 2000 and the open space was converted into John Bartram Memorial Park in honor of the botanist and Darby native.

[16] A $1047 Pennsylvania Growing Greener grant was given to Delco Anglers and Conservationists for riparian restoration on Darby Creek.

In 1997, a $60,000 grant was given to the Darby Creek Valley Association and DelCo Anglers and Conservationists for developing a conservation plan.

[7] In 2001, the U.S. Environmental Protection Agency (EPA) placed Lower Darby Creek Area on the National Priorities List due to contamination from the Folcroft and Clearview landfills.

In 2011 and 2012, the EPA removed approximately 4,000 tons of soil contaminated with polychlorinated biphenyls (PCBs) and shipped it elsewhere for disposal.

In 2016 and 2017, the EPA conducted an additional remediation which involved the removal of approximately 3,000 cubic yards of soil from 33 residential properties due to contamination with PCBs.

The catch per unit effort per hour rate for redbreast sunfish was 123, the highest of several warmwater streams tested during the survey.

Fish species such as mummichogs, silvery minnows, striped bass, and white perch were found at the head-of-tide of the creek.

At the John Heinz National Wildlife Refuge, which is a tidal estuary along the creek, supports various plant and animal species and is a critical migratory habitat for waterfowl.

[21] Plant species of concern at the Darby Creek Mouth Mudflat include Amaranthus cannabinus, Baccharis halimifolia, Bidens bidentoides, Bidens laevis, Eleocharis obtusa, Eleocharis parvula, Heteranthera multiflora, Lycopus rubellus, Pluchea odorata, Sagittaria calycina, Sagittaria subulata, Schoenoplectus fluviatilis, and Zizania aquatica.

In the wetlands at this site, the main tree species include scattered black willow and silver maple.

There are also patches of silky dogwood and wild rose, which are surrounded by assorted wetland plants, including herbs, grasses, sedges, and rushes.

[28] There are many public parks that line Darby Creek, with some having large recreation areas with athletic fields for baseball, soccer, and football, and others containing woodlands and nature trails.

There are a total of eight golf clubs bordering the creek, featuring some of the largest stretches of undeveloped land in the watershed.