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, undammed the entire length of its mainstem, 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.