It is the U.S. Army Corps of Engineers operation of a huge dam and reservoir system on the Missouri that changed the shape and ecology of the river. Today, 35 percent of the Missouri River is impounded, 32 percent has been channelized, and only 33 percent is unchannelized.

Gavins Point Dam on the Missouri River in South Dakota (Photo courtesy American Rivers)

Each year since 1986, American Rivers has released the America's Most Endangered Rivers report to highlight rivers where imminent harm can be avoided or where ongoing destruction can be stopped. In the spirit of the FBI's "Ten Most Wanted" list, the report identifies dangers to rivers that can be avoided if action is taken. It is not a list of the nation's most chronically polluted rivers, the group says.

Four of the endangered rivers were placed on this year's list because of ongoing or proposed U.S. Army Corps of Engineers water projects. The Big Sunflower River in Mississippi, at number two, is threatened by a pair of Corps projects. The White River in Arkansas, at number five, is threatened by the Corps' plans to build an enormous irrigation project and hundreds of navigation structures. The Apalachicola River in Florida, at number 11, is being destroyed by the Corps' efforts to maintain a shipping channel for commercial barges that is rarely used, American Rivers charges.

Topping the American Rivers most endangered list for 2002, the Missouri River drains one-sixth of the United States. It flows 2,341 miles from its headwaters in the Rocky Mountains at the confluence of the Gallatin, Madison, and Jefferson rivers at Three Forks, Montana, to join the Mississippi River at St. Louis, Missouri.

The basin is home to about 10 million people from 28 Native American tribes, 10 states - Colorado, Iowa, Kansas, Minnesota, Missouri, Montana, Nebraska, North Dakota, South Dakota, Wyoming - and a small part of Canada.

The Missouri River reservoir system is the largest in the United States with a storage capacity of 74 million acre feet and a surface area exceeding one million acres. The six dams built in Montana, Nebraska, North Dakota and South Dakota transformed one-third of the Missouri River ecosystem into lake environments.

Missouri River in flood, April 6, 1999. Looking southeast toward St. Louis, Missouri (Photo courtesy U.S. Army Corps of Engineers)

Great quantities of sediment and organic materials flow into the reservoirs and are trapped behind the dams, reducing reservoir storage capacity and sediment transport below the dams. Dams block native fish migration to spawning grounds and modify the flow regime in the river system.

In its report, American Rivers cites these dams and other Corps of Engineers water projects as a leading threat to rivers nationwide. The organization is urging Congress to pass legislation that will "put a stop to the agency's wasteful and destructive practices."

The Missouri River ecosystem is in "a serious state of decline," and the ecosystem faces the prospect of "irreversible extinction of species," the National Research Council of the National Academy of Sciences reported in January. Congress should enact legislation to ensure that federal officials manage the river in a way that improves ecological conditions, says the committee that wrote the report, "The Missouri River Ecosystem: Exploring the Prospects for Recovery."

American Rivers lists the other nine most endangered rivers in the United States as:

Big Sunflower River (Photo by Louie Miller courtesy American Rivers)

• Big Sunflower River, Mississippi, Corps flood control projects Unless the public speaks out and environmental regulators exercise their legal authority, the organization warns, construction crews working for the Corps of Engineers will soon begin work on a pair of projects that will "scrape the heart out of Mississippi's Big Sunflower River and drain and damage over 200,000 acres of its surrounding wetlands." The Corps is proposing to spend more than $250 million to help large landowners increase production of surplus crops on marginal agricultural lands.

• Klamath River, California and Oregon, water supply and quality In the drought prone headwaters of the Klamath River, the Bureau of Reclamation is attempting to maximize irrigation deliveries even though the diversions and polluted agricultural runoff are causing the river's ecosystem to collapse. Salmon populations have dropped to less than eight percent of their historic averages. Dwindling fisheries threaten the livelihoods of commercial fishermen and local communities, as well as the treaty rights of several Indian tribes.

• Kansas River, Kansas, non-source pollution Thirty years after the Clean Water Act became law, the state of Kansas has given up its effort to clean up the agricultural runoff polluting its namesake river - passing a law intended to strip away the Act's water quality standard protections from nearly all its waters. American Rivers fears that "agricultural lobbyists across the country will seek to copy the state's example, and the Kansas River will continue to fester under a smothering load of livestock manure."

• White River, Arkansas, Corps navigation The Corps of Engineers has started work on an enormous irrigation project that will suck more than 100 billion gallons of water from the White River each year, and is also proposing to construct hundreds of wing dikes along 250 miles of the lower river, to improve navigation for commercial barges.

• Powder River, Wyoming, coal bed methane The growing coal bed methane industry in the Powder River basin means too much low quality water is entering the river at the wrong time of year. With at least 51,000 methane gas wells anticipated by 2010, public officials must ensure that coal bed methane development proceeds responsibly and that its byproduct water is properly managed to protect the Powder River and its tributaries.

• Altamaha River, Georgia, water withdrawal With projected population growth topping 300 percent for some communities in coming years, Metro Atlanta's demand for services such as drinking water and electricity threatens to overwhelm the Altamaha River.

  

  Sunset on the Allagash River, Maine (Photo courtesy American Rivers)

• Allagash River, Maine, wild and scenic violations Once the crown jewel of the nation's Wild and Scenic Rivers System, the Allagash Wilderness Waterway has lost much of its primitive character to "decades of neglectful management," American Rivers says. Some Maine legislators have introduced a proposal to strip away the protections that federal wild and scenic river designation affords.

• Canning River, Alaska, oil and gas development Alaska's Canning River marks the western border of the Arctic National Wildlife Refuge. Should the U.S. Senate follow the House of Representatives and vote to allow oil and gas exploration and drilling in the refuge, the industry would pump millions of gallons of water from lakes in the Canning River delta, dig huge gravel mines in its floodplain, and disturb wildlife. A destructive oil spill is always a possibility.

• Guadalupe River, Texas, water withdrawal The Guadalupe River and its tributaries are threatened by growing demand for their water. A conservation organization is seeking to preserve the ecological resources and rural economy the river sustains by securing water rights which it will leave in the river. If the state of Texas awards the remaining water rights to developers instead, the river's water will be siphoned off and sold to the detriment of commercial and recreational fisheries, and a group of endangered whooping cranes.

• Apalachicola River, Florida, Corps dredging In an effort to maintain a commercial shipping channel that is barely used, the Corps of Engineers is destroying Florida's Apalachicola River by scouring the river bottom, dumping the dredge material in sensitive habitat, and aggressively manipulating the flow. The Corps itself has conceded that its efforts are not "economically justified or environmentally defensible." Rather than pour more money into this project, American Rivers says Congress should de-authorize it altogether in the Water Resources Development Act of 2002.