In many parts of the world, concern for the quality of fresh water is leading citizens and politicians to clean up waterways that have been damaged by human activities. In the United States many of the worst sources of industrial pollution have been stopped. Still, many experts agree that rivers world-wide need help in a variety of ways. Learning about the state of the world's rivers is important in our efforts to improve the rivers in our back yards. 

Learning about the world's rivers is important in our efforts to improve the rivers in our back yards.

"There's even a greater threat to biodiversity in rivers than there is on land," says Peter Moyle, a professor of Fisheries at the University of California at Davis who has studied the world's major river systems. "No matter how bad things are on land, you'll find that they're worse in nearby rivers." Though industrial and urban pollution contribute significantly to this problem, of even greater concern are the alterations humans have made in the character and course of rivers around the globe.

The "Mississippi Model"
Changes to the course and character of the Mississippi River, which has been described as the greatest engineering project in the history of civilization, is a prime example. The Mississippi's ever-shifting, braided channels have been merged and deepened through the construction of wing dams and the work of dredging operations. Its wildly fluctuating flow is now regulated by more than thirty locks and dams. Fourteen hundred miles of levees prevent flooding in lowland areas. To allow access for oil exploration and drilling, 10,000 miles of channels criss-cross the delta's fast-disappearing freshwater marshes--the most productive wildlife habitat on earth, according to one U.S. Fish and Wildlife Service expert. 

This approach to river management continues to be followed on rivers around the globe. As knowledge of river systems grows, however, the ecological problems resulting from the "Mississippi model" become more apparent. "The problems you see in the Mississippi, such as the health of large migratory fish populations, are seen elsewhere," says Moyle. "Fish like the sturgeon are in trouble all over the world because of the alteration of river habitats and pollution." The Mississippi's lock and dam system blocks sturgeon from reaching their upstream spawning grounds. Even if the adults were able to spawn, levees would prevent their offspring from maturing on the river's biologically rich floodplains, which formerly were covered by annual floods. Also, the widespread practice of removing downed trees that interfere with navigation has destroyed vast habitats for aquatic insects, which many fish depend on for sustenance. 

Pollution compounds matters further, says Moyle. "Many species are surprisingly resilient and bounce back from major pollution spills, but they have great trouble with chronic sources of pollution." PCBs and chlorinated fluorocarbons--the main culprits--usually don't kill fish outright, but they collect in the fat of adult fish and interfere with reproduction. 

The Mississippi Model in Bangladesh 
A controversial Mississippi-inspired plan in Bangladesh would construct levees to reduce the effects of flooding on the Ganges River delta, where cyclones and severe floods in 1987 and 1988 resulted in terrible destruction and loss of life. The levees are being promoted as a way to safeguard human lives while opening up fertile delta lands to farming. They are an attempt by some in Bangladesh to exert some control over a river system that enters their borders already suffering from deforestation and damming upstream in Nepal, India and China. 

Jim Wescoat, Assistant Professor of Geography at the University of Colorado, says that the planned levees are likely to be unsafe and ultimately unsustainable. Also, the long-term environmental costs of the project outweigh any short-term economic gains from creating more fertile farmland. "The levees would encourage people to occupy even more vulnerable areas, and if the structural system would fail [which is likely given environmental conditions upstream] we'd see even greater disaster," Wescoat says. 

Saltwater introduced by the channelization of the river would destroy sensitive freshwater marsh habitats that serve as nurseries for shellfish--a process occurring now on the Mississippi delta. This could destroy the Ganges delta's traditional fishing economy and further threaten a beleaguered mangrove ecosystem called the Sundarbans, which is habitat for the Bengal tiger. Eventually, Wescoat says, channelization would even destroy the farmlands that it seeks to create. Without the deposits of fresh silt made by the annual floods, delta farmlands would be lost to coastal erosion and a process called subsidence, whereby muddy soils deposited as river silt slowly sink and spread out under their own weight. 

A Dam on the Amazon 
The largely untamed Amazon River, by almost any measure the largest river with the largest watershed in the world, has yet to suffer many of the assaults visited upon other river systems. Thus it provides an opportunity for Brazilians, who occupy much of the river's watershed, to exercise wise management. 

At the same time, deforestation threatens to increase flooding and siltation. And research conducted by the International River Network (IRN) has identified the Tucurui dam on the Tocantins River, an Amazon tributary, as an illustration of the problems that can accompany the construction of large dams. 

The 1,400 megawatt Tucurui dam, completed in 1984 to provide power for an aluminum smelting plant, flooded a large area of standing rainforest. The resulting stagnant backwaters proved perfect for breeding such huge quantities of malaria-infested mosquitoes (studies assessed average bite rates of 500 per minute) that the area has become uninhabitable. The water released from the dam is completely depleted of oxygen. As a result, fish populations in the lower Tocantins have been extinguished. 

To combat problems like this in the world's freshwater ecosystems, the IRN works with international lenders like the World Bank to encourage them to not support large-scale, ecologically destructive water projects. Such international efforts combined with active and informed citizens working to preserve the rivers that sustain them may represent the best hope for the earth's flowing waters. With awareness and a commitment to take action, we can improve conditions in damaged rivers and help those still running clean and free to stay that way.

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