Discover the Central Passaic Basin

National Treasures of Geologic Wonder

The Geological Story of Lake Passaic

Over the period of the last ice age, the massive Wisconsin Glacier carved its way across this area, leaving behind a vast proglacial lake, Glacial Lake Passaic. The glacier’s meltwater pooled in the Central Passaic Basin, creating Glacial Lake Passaic—a sprawling lake covering an area larger than many modern cities. At its peak, the lake stretched over 300 square miles, bordered by the Watchung Mountains to the east and the Highlands ridges to the west. As the glacier receded, natural gaps formed in the mountains and ridges, allowing the lake to drain. Over time, the lake left behind sedimentary deposits that now underpin the basin’s wetlands and floodplains. These glacial legacies remain visible today in the form of moraines, gorges, ancient river channels, and in thick layers of sediment (some at depths of over 300 feet).

The Central Passaic Basin Today

Nestled amidst the bustling suburbs of northern New Jersey, the Central Passaic Basin provides a crucial refuge for biodiversity and an important resource for local communities. Spanning over 30,000 acres of wetlands and forest, fed by tributaries such as the Whippany and Rockaway Rivers, the basin serves as a natural flood buffer, absorbing and storing excess water during heavy rains. The area’s unique hydrology protects thousands of residents from the most severe impacts of flooding while also providing clean drinking water for locations as far as Jersey City. 

Beyond its importance to the surrounding urban areas, the basin is an ecological treasure. The basin is home to red maple (Acer rubrum) swamps, marshes comprised of cattails (Typha spp.), bulrushes (Scirpus spp.), sedges (Carex spp.), and arrow arum (Peltandra virginica), as well as open grasslands all which provide essential habitats for hundreds of plant and animal species, including rare and endangered ones like the Indiana bat and swamp pink. The basin’s sprawling landscapes act as a refuge for wildlife in one of the most urbanized regions in the United States, offering both a sanctuary for nature and a place for human recreation and reflection. 

A Biodiversity Hotspot in an Urban Environment

Today, the Central Passaic Basin encompasses more than 30,000 acres of wetlands, including swamps, marshes, and upland forests, and harboring a rich array of species. Notwithstanding its close proximity to densely-populated urban areas, the Central Passaic Basin is a sanctuary for over 600 plant species, including the federally listed swamp pink (Helonias bullata) and for hundreds of species of animals, including rare wildlife such as Indiana bat (Myotis sodalis) and blue-spotted salamander (Ambystoma laterale), as well as over 100 bird species of conservation concern. The forested swamps and marshes provide critical breeding grounds for amphibians and waterfowl, stopover habitat for migrating songbirds, and a prey base for raptor populations. The basin is home to over a hundred species of breeding birds, including many species of conservation concern. The wetlands act as a natural sponge, mitigating flood impacts while sustaining hundreds of plant species. Visitors can marvel at these ecological treasures while appreciating the critical role the wetlands play in maintaining regional biodiversity.

Challenges and Conservation Efforts

The Central Passaic Basin is not without its conservation challenges. Over half the region is developed, and its wetlands are fragmented by highways and utility corridors. The density of suburban sprawl has introduced pollutants and degraded water quality. Despite its ecological significance, the basin faces numerous problems associated with sprawl, including historic and contemporary pollution (including four Superfund sites), disruption to the geography and hydrology from development and waste treatment plants, and ecological changes from introduced species like purple loosestrife (Lythrum salicaria) and the common reed (Phragmites australis). Flooding remains a persistent issue, with nine major floods since the 1960s leading to federal disaster declarations. 

However, conservation efforts—including initiatives led by private landowners, state regulations, and the work of organizations like the U.S. Fish and Wildlife Service—aim to protect and restore these critical habitats. These efforts include:

• Floodplain Management: Regulations like New Jersey’s Flood Hazard Control Act protect vulnerable wetlands that retain floodwaters, mitigating damage from future floods. Special provisions for the Central Passaic Basin ensure no net loss of floodwater storage capacity.
• Waste Disposal Regulation: Laws now prohibit indiscriminate dumping, a practice that once left the basin with a legacy of contamination. Efforts include cleaning up Superfund sites and improving water quality through stricter sewage discharge standards.
• Land Acquisition Programs: Over 20,000 acres of land in the basin are now protected, including parcels purchased through state and federal programs to conserve critical flood storage areas and biodiversity hotspots.
• Restoration Projects: Initiatives like wetland restoration, invasive species removal, and habitat enhancements for rare species are ongoing, supported by partnerships and settlement funds from polluters.

Visitors can also learn about community-led efforts to combat pollution and protect habitats by exploring the basin’s many natural wonders.

Experience and Protect

The basin contains an impressive number of National Natural Landmarks (or NNLs), National Parks, and a National Wildlife Refuge for such a relatively small geographical area. NNLs like the Great Swamp National Wildlife Refuge and Moggy Hollow Natural Area invite visitors to experience the basin’s natural beauty. Whether you’re a hiker exploring its rugged gorges or a birdwatcher marveling at its numerous avian inhabitants, the Central Passaic Basin is a reminder of nature’s resilience and our responsibility to preserve it for future generations. Here are some of the many great places to visit and experience the Central Passaic Basin:

• Paterson Great Falls National Historical Park: Explore the dramatic basalt cliffs of this National Historic and Natural Landmark, where glacial waters once carved a path through ancient lava flows, now a scenic reminder of the basin’s geologic history. It features a large brick building that houses an historic hydroelectric plant that still generates power today!
• Great Swamp National Wildlife Refuge: A vast 7,600-acre refuge offering tranquil hiking trails, birdwatching opportunities, and an immersive look at the region’s diverse wetland environments. This NNL is a sanctuary in a mostly suburban landscape that offers an important resting place for numerous species of migratory birds.
• Moggy Hollow Natural Area: Known for its steep ravines and marshy landscapes, this NNL is a rugged preserve that showcases the outlet of ancient Glacial Lake Passaic and offers a challenging but rewarding experience for intrepid hikers.
• Troy Meadows: This NNL is a vast freshwater marsh that serves as a critical stopover for migratory birds and supports a variety of wildlife, making it a top destination for nature enthusiasts and photographers.
• Morristown National Historical Park: Combining natural and historical significance, this park offers lush landscapes shaped by glacial activity and a rich Revolutionary War history to explore.

From exploring breathtaking landscapes to learning about its ecological significance, these sites offer inspiration and a call to action for preserving the Central Passaic Basin.

Get Involved

Visitors and residents alike can contribute to the basin’s protection:

• Join habitat restoration projects to combat invasive species.
• Participate in citizen science initiatives, such as bird counts and water quality monitoring.
• Donate or volunteer with organizations working to conserve this vital ecosystem.

The Central Passaic Basin is more than just a recreational space—it is a critical habitat and important place of conservation and environmental management. By exploring, learning about, and contributing to its preservation, we ensure that this vital ecological and historical resource thrives for many generations to come.

Tour the Central Passaic Basin Online (Using Our Interactive Map)

Resources and Additional Information

This page was developed in partnership with the National Natural Landmarks Program of the U.S. National Park Service and by sourcing information from the following references. These sources contain additional information about the ecological, geological, social and cultural aspects of specific cites as well as the basin as a whole.

Works Consulted

“Great Falls of Paterson-Garret Mountain.” U.S. Department of the Interior. (n.d.). National natural landmarks. National Parks Service. https://www.nps.gov/subjects/nnlandmarks/site.htm?Site=GRFA-NJ 

“Great Swamp.” U.S. Department of the Interior. (n.d.). National natural landmarks. National Parks Service. https://www.nps.gov/subjects/nnlandmarks/site.htm?Site=GRSW-NJ

“Moggy Hollow Natural Area.” U.S. Department of the Interior. (n.d.). National natural landmarks. National Parks Service. https://www.nps.gov/subjects/nnlandmarks/site.htm?Site=MOHO-NJ

“New Jersey’s Central Passaic Basin Prehistoric Glacial Lake, Present-Day Wetland Treasure.” (2007). U.S. Fish & Wildlife Service. https://www.fws.gov/media/new-jerseys-central-passaic-basin-prehistoric-glacial-lake-present-day-wetland-treasure

“Troy Meadows.” U.S. Department of the Interior. (n.d.). National natural landmarks. National Parks Service. https://www.nps.gov/subjects/nnlandmarks/site.htm?Site=TRME-NJ

“Riker Hill Fossil Site.” U.S. Department of the Interior. (n.d.). National natural landmarks. National Parks Service. https://www.nps.gov/subjects/nnlandmarks/site.htm?Site=RIHI-NJ