Vital waterways for people and wildlife

Home to crocodiles, freshwater sharks, barramundi and hundreds of other fish species, the rivers of New Guinea rival terrestrial ecosystems in terms of complexity and diversity. They are also integral parts of forest ecology.

Some of the world’s great rivers flow through the island's forests including the Asmat and Mamberano River in Indonesia's Papua Province, and the majestic Sepik River and lake country in Papua New Guinea (PNG).

A bird’s eye view of New Guinea’s river systems

River systems form extensive floodplains at lower altitudes, arising from networks of progressively smaller rivers and streams originating in the highlands.

In southern PNG, rivers flowing towards the Gulf of Papua have created large deltas, forming significant areas of estuaries with brackish water and extensive mangroves. Rivers in the north generally flow into the Bismarck Sea. There are no deltas and inland estuarine areas are almost absent.¹

Freshwater biodiversity

The rivers of New Guinea swell with species numbers.Within the enormous southward-flowing Fly River alone, there are over 100 fish species, representing 33 families.²

New Guinea's freshwater species include bull sharks, sawfish and large saltwater crocodiles. Barramundi and certain other freshwater species are of great economic importance as commercial food sources.

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The Sepik River

Over 900 km long, the Sepik River forms the largest unpolluted freshwater system in New Guinea. It is also one of the largest and most intact freshwater basins in Asia-Pacific.

The river's pristine state is due to the absence of large cities and development projects, and therefore few human-induced impacts in the Sepik region.

The diverse habitats and extensive lake systems of the Sepik Basin support important water-bird and crocodile populations. The Sepik River is home to approximately 500,000 people who depend almost entirely on products from the rivers and forests for their livelihoods.

Although development is limited, several factors tarnish this idyllic setting. Unsustainable industrial logging, invasive species and proposed mining developments are constantly threatening the integrity of the area.³

Fly River

The Western Province of PNG is bisected by the Fly River, the largest of its kind in terms of water flow in Australasia. In terms of the colossal amounts of water it discharges, the Fly is comparable to the Niger and Zambesi Rivers in Africa and the Danube in Europe.

The Fly River and its major tributary, the Strickland River, flow for over 1,200 km. Another major tributary of the Fly River is the Ok Tedi, which has been heavily impacted by the Ok Tedi mine.⁴

Some of the most diverse fish fauna in Australasia
The Fly River carries some of the most diverse fish fauna in Australasia. Approximately 128 fish species, representing 32 families, have been recorded from the Fly River system. Of these, 17 species are found nowhere else.

Many of the freshwater fish in this river system, including barramundi (Lates calcarifer), tarpon (Megalops cyprinoids), mangrove jack (Lutjanus argentimaculatus), mullet and eels, undertake extensive migrations, regularly moving between freshwater and estuarine areas for feeding and/or reproduction.

The impact of El Niño droughts, introduced species and mining operations (such as the Ok Tedi copper mine) have negatively affected fish populations and fisheries of the Fly River system.⁵

The Mamberamo River

The Mamberamo River is a large river in the Indonesian province of Papua. Starting from the confluences of its upper tributaries, the Mamberamo continues its northwards descent along a great valley before reaching the marshes of a broad delta.

The Mamberamo discharges into the Pacific Ocean at the northern point of Point D'Urville in Indonesia.⁶

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¹ Coates, D. 1989. Review of Aquaculture and Freshwater Fisheries in Papua New Guinea. FAO. PNG/85/001 Field Document No. 1.
² WWF. New Guinea Rivers & Streams - A Global 200 Ecoregion. Accessed online 11/01/2006.
³ WWF. Undated. Umaand Me’haWildlife Management Areas: Niksek River, East Sepik Province, Papua New Guinea. Leaflet.
⁴ VIMS. Fly River. Accessed 12/01/2006.
⁵ Swales, S. Undated. Fish and Fisheries of the Fly River, PNG: Population Changes Associated with Natural and Anthropogenic Factors and Lessons to be Learned. World Fisheries Trust / IDRC /UNEP. 26 pp.
⁶ Wikipedia. Mamberamo River. Accessed 12/01/2006.