An estuary, not just a river
Near Camden, the Delaware is tidal and influenced by the ocean, which makes it an estuary: a place where fresh water from upstream mixes with salt water from the bay. Further downstream toward Delaware Bay the water becomes brackish and then salty, while around Camden and Philadelphia it is mostly fresh or only slightly brackish, depending on tide and rainfall. This gradient is a main reason the river supports such a mix of species.
The river is also a heavily used industrial and urban waterway. Wildlife here does not live in a pristine setting, and this article describes what can commonly be seen rather than promising particular sightings.
Fish
The tidal Delaware has long been a migration route for fish that move between the ocean and freshwater.
- American shad are the best-known example. They are migratory fish that run up the river in spring to spawn, and their history is tied to a long-running fishery. Their numbers declined during the period when the river was badly polluted and have been described as recovering in later decades, though changes are not uniform.
- Striped bass are a popular sport fish that also use the estuary seasonally.
- Atlantic sturgeon and shortnose sturgeon are large, long-lived fish that are protected under federal law. They are rarely seen by the public, and conservation concern has been significant.
- Blue crabs, catfish, white perch, eels and a range of smaller fish use the tidal river and its marshes.
Anglers should check current state regulations and advisories, as rules on seasons, size limits and consuming fish from urban waters are issued by official agencies and change.
Birds
Birds are the most visible wildlife on the tidal Delaware, in part because the river lies along a major route used by migrating birds up and down the Atlantic coast.
Common sights include gulls, cormorants, Canada geese and mallards on the water, and herons and egrets in shallows and marshes. Ospreys, which feed on fish, return in spring, and bald eagles, once very rare in the region, are now reported more often in the lower river corridor than they were decades ago. Winter often brings additional waterfowl, such as ducks resting on open water.
Farther down the estuary in Delaware Bay, the spring gathering of migrating shorebirds on beaches where horseshoe crabs lay eggs is a well-documented event. It occurs roughly in May and is an example of how the estuary supports travelers from very distant places. It is not a Camden-area sight, but it is part of the same system.
Marshes, mudflats and other habitats
Animals need more than open water. Tidal marshes, mudflats and shallow creek mouths provide feeding grounds and shelter. Along the lower river, much of this habitat was filled in, diked or built over as ports and industry expanded. What remains, along with restored sites, can matter far more to wildlife than its size suggests.
Reptiles, amphibians and mammals also live in the river corridor. Turtles, muskrats and deer can turn up along creeks and in parks, and the Cooper River and its park corridor is one place where people encounter local wildlife without leaving the suburbs.
Seasonal changes
A rough calendar helps visitors understand why the river looks different at different times of year.
- Spring: fish runs begin and migrating birds pass through. Ospreys return to nesting platforms.
- Summer: warm water and long days favor crabs, young fish and nesting birds. Algae and low oxygen can be concerns in hot, dry spells.
- Fall: a second wave of migrating birds moves south, and fish begin moving back toward the ocean.
- Winter: waterfowl gather on open water, and some fish are less active. Ice can limit what is visible.
Exact timing varies from year to year with temperature and weather.
Wildlife and water quality
The presence of fish and birds is often discussed as a sign of river health, but it is an imperfect one. Some species are tolerant of poor conditions, and others can return while contaminants remain in sediment. The broader subject is covered in the piece on water quality, which looks at how rivers recover from pollution.
Parks and green spaces along the river provide public access, and visitors can help by keeping a respectful distance, never feeding wild animals and keeping pets controlled. Because conditions and access change, check with the managing agency for current rules before visiting a wildlife area.