Adjacent to Philadelphia International Airport, the refuge protects the largest remaining freshwater tidal marsh in Pennsylvania.

In the late 1760s, it was discovered by the Darby Society of Friends that the Elliot family was running a slave plantation on Smith Island.

In his will, he gave a pension, a house, and 2 acres of land at Smith Field (now part of Tinicum Wildlife Preserve) to his slave Old Primus, who was freed immediately.

His son, Christopher, tried to circumvent the will and was sued by Quakers Thomas Shipley and Isaac Hopper, working through The Pennsylvania Anti-Slavery Society.

In 1953, Allston Jenkins, a birdwatcher who lived in the Chestnut Hill section of Philadelphia, learned of Gulf Oil's plans to dredge the Schuylkill River and dump the spoils into the Marsh.

The areas of open water along with the adjacent heavily vegetated tidal wetlands, formed an ideal habitat for thousands of migratory birds.

[1] They worked together to begin a long series of legal injunctions, public hearings, and extraordinary efforts that stopped both the highway's rerouting and the landfill's operation.

In addition to the above-mentioned there are a wide variety of fish species that can be found in both, Darby Creek, the lifeblood of Tinicum Marsh, as well as the 145 acre (0.6 km2) impoundment and the smaller, Hoy's Pond.

They include brown bullhead, channel catfish, crappie, carp and small striped bass that utilize the wider expanses of Darby Creek, just before its confluence with the Delaware River, in the earlier stages of their development.

Migratory birds like warblers, egrets, sandpipers, and a large variety of ducks, within the Atlantic Flyway, use the refuge as a resting/feeding spot during spring and fall flights.

In addition, deer, opossums, red foxes, raccoons, coyotes, beavers, river otters, minks, woodchucks, and muskrats take refuge here along with a wide variety of wildflowers and plants.

Bats are frequently observed by visitors on the refuge during warmer seasons and a formal species diversity and population survey would provide valuable information on recent declines of these important creatures due to white nose syndrome and habitat disturbances.

There are several species of reptiles and amphibians that call the refuge home including the northern water, garter and DeKay's brown snakes; pickerel, wood and southern leopard frogs (the latter listed as endangered in Pennsylvania) and the state threatened American red-bellied turtle as well as the painted, snapping and eastern box turtles.