Nature & Science

Scenic view of the Upper Delaware River.

David B. Soete

The Delaware River is one of the last large free-flowing rivers left in the contiguous 48 states, and one of the last major rivers without any dams or control structures on its main stem. It is the longest undammed river east of the Mississippi and extends 330 miles downstream from the confluence of the East and West branches in Hancock, New York to the mouth of the Delaware Bay where it empties into the Atlantic Ocean. The river is fed by 216 tributaries, the largest being the Schuylkill and Lehigh Rivers in Pennsylvania. In all, the basin contains 13,539 square miles. More than 180 miles of the 330-mile-long Delaware River have been placed into the National Wild and Scenic Rivers System; this includes all 73.4 miles of Upper Delaware Scenic and Recreational River.

The Upper Delaware River exhibits some of the highest ecological integrity found in any of the large rivers of this region. As the least developed section of the last major river on the Atlantic Coast, the Upper Delaware's wild and scenic, largely ecologically intact, free-flowing character supports key components and processes that contribute to the superb natural resources found here.

Exceptional water quality, resulting from a predominately forested landscape, sustains high quality fish and aquatic insect assemblages. Excellent in-channel conditions result in an abundance of riffles, runs, and pools, and a diversity of in-stream habitats. These aquatic conditions, combined with good riparian habitat that is coupled with a functioning floodplain, provides great hydrological connectivity, structure, and function.

The Upper Delaware River's ecological value extends beyond this segment of river. It provides regionally important high quality historic spawning and rearing habitat for sea-run migratory fish, helping to buttress their larger range-wide populations. These sea-run migratory fish greatly benefit the river as well. The spring spawning run of American shad brings fish that are a storehouse of carbon and nutrients amassed over their multi-year ocean odyssey into the river, providing nourishment that energizes the system and coincides with critical reproduction and provisioning periods for its wildlife, such as bald eagles. Sea-run American eels serve as a keystone species here, as the primary host fish (enabling reproduction) of eastern elliptio mussels, which make up the greatest animal biomass in the Delaware River and play an integral role in contributing to water quality through their filtering capacity.