Rivers: Dams, Canals and Channeling: Page 1 Endangered Species Handbook

Aquatic Ecosystems

Rivers: Dams, Canals and Channeling: Page 1

Between 1973 and 1983, Brazil borrowed $30 billion Brazil from international funds, such as the World Bank, to construct these dams (Lanz 1995). Huge debts are incurred by poor countries borrowing money from international funds to pay for dams. The real profits from dams accrue to companies that construct them and industries that directly benefit (Lanz 1995). Yet the rationale for dams has traditionally been to benefit the population as a whole. Numerous extinctions of native wildlife and plants have resulted from dam construction. This makes the real cost of such cheap electricity far more expensive, yet such calculations are not considered when nations endorse dams.

Until the 20th century, all but a few of the world's major rivers were pure. Today, the opposite is true. Unpolluted, un-dammed rivers are the exception, and even the great diversity of the mighty Amazon River is now threatened by dam construction on its tributaries. These dams have endangered countless species of wildlife. The majority of species evolved to live in rivers are unable to adapt to conditions created by artificial barriers such as dams and resultant changes in water temperature and current. In the United States, only 2 percent of rivers remain free-flowing and undeveloped (Barlow 1999). All major European rivers have been dammed, diked or channeled. After dam construction, reservoirs, which often cover hundreds of square miles, gradually fill, drowning untold thousands of animals in the process. Even those able to swim to dry land rarely survive because territories are already occupied by members of their own species. In tropical forests, threatened monkeys, armadillos, rodents, snakes and other animals drown, and rare plants and trees die under hundreds of feet of water. Dam gates cause wildlife mortality as well. Endangered West African manatees (Trichechus senegalensis) have been crushed to death when caught in the giant gates of these dams, or left high and dry when water levels were lowered (Reynolds and Odell 1991).

Dams upriver from coastal marshes disrupt the flow of water, which can cause crashes in breeding fish populations. Dammed rivers that empty into coastal deltas experience reduced freshwater flow, which creates an influx of saltwater into freshwater marshes (Lanz 1995). This devastates fisheries adapted to low salinity, such as many species of shrimp and crayfish. An extreme case is in Louisiana; its entire marsh coastline and its $700 million-per-year fishery-based economy have collapsed over the past few decades as saltwater has crept into freshwater marshes, drowning 1 million acres a year. Dikes and levees built for shipping traffic on the Mississippi River and its tributaries have decreased the freshwater flow into the marshes, causing this disaster. Another negative effect of dams on coastal ecosystems is the blockage of silt and sand that enriches delta marshes and maintains sandy beaches. Dams generally have to be abandoned within about 50 years because they fill up with silt and can no longer function efficiently. The serious environmental damage caused far outweighs these short-term economic benefits.

Migratory fish, from salmon to sturgeon and shad, find their paths blocked by dams. They leap in vain at the concrete barriers, and most fail to negotiate fish ladders on those dams that have installed these devices. The young of salmon that manage to hatch upstream from dams are crushed and torn to bits in the dams' massive turbines, which kill 90 percent of salmon young each year in the Pacific Northwest of the United States. Virtually every species of the seven salmon native to this region is threatened with extinction, and 214 stocks are threatened; 106 populations have already disappeared (Stein et al. 2000). These salmon and steelhead trout have also suffered from siltation caused by logging and agriculture, which has clouded the clear streams needed for spawning. The loss of these salmon, which numbered in the billions when Lewis and Clark entered the region in the early 19th century, has affected the livelihoods of hundreds of fishermen and wildlife that depended on these fish. Bald eagles, black and grizzly bears, river otters and many bird species rely on these fish as a vital food resource. Each fall, bears eat large quantities of fish, especially fatty fish like salmon, to fatten up prior to their winter hibernations. Without these fatty stores, many bears do not survive the winter.

The outflow from dams is regulated by opening of gates, resulting in flows ranging from trickles to torrents. Wildlife requiring a certain water level can be eliminated when it changes radically. Rare trumpeter swans (Cygnus buccinator) wintering in eastern Idaho died in large numbers in 1989 when the reservoir on the Henry's Fork tributary of the Snake River was closed during a drought. The water downstream had previously remained unfrozen in winter, providing vital habitat. In February 1989 when the water froze as much as 4 feet below the surface, more than 50 swans froze or starved. The surrounding community became so concerned they raised $30,000 to purchase 4 billion gallons of reservoir water to be released. Life magazine photographer Glenn Oakley documented locals picking up and carrying the surviving swans to indoor areas; some were even warmed in nearby bathtubs. These swans were then transferred to a rehabilitation center where they were kept throughout the rest of the winter, and grain was supplied to the weakened swans remaining in the wild (Life April, 1989). In the words of a rescue coordinator from the Idaho Department of Fish and Game, "I guess nobody ever told these swans they should have filed for water rights."

Even more tragic events took place in Canada, where a massive dam project has inundated some 4,000 square miles of forest land and riverine habitat in Quebec and Labrador. These dams have had major effects on both people and wildlife since the 1970s. They impeded the ancestral migration route of caribou and caused 10,000 of these animals to drown in a torrent of water from one of the new dams in 1990 (Verhovek 1992). Chief Matthew Coon-Come of the Grand Council of the Crees appealed to conservationists to assist tribes in stopping any further work on the dam system. "For 5,000 years we did not leave a trace of our having been in James Bay. What we had came from the land and went back to the land. The land is sacred to us. This land holds the graves of our ancestors. But now, Hydro-Quebec is destroying our sacred land and our way of life. If you were to fly with me today in a Cessna, starting from the first James Bay dam, we'd fly for four and a half hours, and all you'd see is land drowned by water, three major rivers destroyed" (Coon-Come 1993). Chief Coon-Come first began fighting the dam projects in 1972 when he was 16 years old, and in 1994, at the age of 38, he was honored as the first North American recipient of a Goldman Environmental for his achievements in stopping the second phase of the James Bay project.

The Indus River dolphin or Susu (Platanista minor) of Pakistan and the Ganges dolphin, which also inhabits the Brahmaputra River system, are highly endangered. These dolphins appear to be blind, but have deeply set eyes that can receive light at an angle, perhaps when they surface (Nowak 1999). Of the two, the Indus River species is more endangered and considered to be on the brink of extinction (Leatherwood and Reeves 1983). It is considered endangered. This dolphin's entire range lies within the Pakistani provinces of Sind and Punjab where, despite of legal protection, it has declined, mainly as a result of a series of dams on the Indus that isolate populations, along with accidental drowning in fish nets and pollution (NGS 1995). Its population has been estimated at only about 400 animals between two dams in the Sind Province, and perhaps 150 more in small subpopulations farther north in the Punjab Province (Nowak 1999). The Ganges River dolphin inhabits a larger range and is found in western India, Bangladesh and Nepal. Pollution, boat traffic, fragmentation of populations by dams, accidental capture in fishing gear and hunting all threaten this species (Nowak 1999). 4,000 to 5,000 Ganges dolphins survive, and the species has disappeared from the Karnaphuli River to the east of the Ganges at the very least (Nowak 1999). In Nepal, dams have blocked portions of the dolphins’ range, trapping them in portions of river too small to ensure their survival (Leatherwood and Reeves 1983).

Fish and mollusks are especially vulnerable to disappearance when their habitats are radically changed by dams. The conditions created in the reservoir usually end in the destruction of aquatic vegetation, bottom-dwelling mollusk fauna, and the fish, turtles, birds and mammals that are part of free-flowing rivers. Sediment soon covers the mollusks and bottom vegetation and kills them, and water currents no longer bring food to the gills of mollusks and keep water clear. Caddis and stone flies, upon which trout and other fish feed, disappear when their larvae do not hatch in reservoir conditions (Lanz 1995). These insects are the primary food for trout and many other fish. Cold temperatures of swift-flowing, tree-lined rivers in temperate areas that teem with trout and salmon become warm, pond-like areas, to which these species cannot adapt.