JEFFERSON CITY, Mo. - A study by a supporter of the barge industry found that endangered birds fare well along the Missouri River, even better than they did 200 years ago.

Environmentalists, however, scoffed at the study's conclusions. They say the river must be changed to protect birds and fish.

Upstream and downstream states have been at odds for years over how to manage the river, which runs 2,341 miles from Montana to St. Louis, where it empties into the Mississippi River.

Montana and the Dakotas want steady or rising water levels in the river's six huge reservoirs during spring to protect the eggs laid in shallow water by walleyes and baitfish. Those fish populations are crucial to multimillion dollar sport fishing industries on the lakes.

Downstream states want water to support barge traffic below Sioux City, Iowa, to prevent floods and to provide water for cities, power plants and other uses.

Environmental groups, meanwhile, want the U.S. Army Corps of Engineers to alter the river's flow to more closely mimic a natural spring rise and summer fall as a way to protect endangered or threatened birds and fish that live downstream from the dams.

A study was released Tuesday by Missouri River Keepers, a Sioux City, Iowa, nonprofit group that says it supports keeping the river viable for purposes authorized in federal law, including navigation, fish and wildlife, water supply and recreation.

The study said that two endangered birds, the least tern and the piping plover, are thriving on the Missouri River. Bill Beacom, of Sioux City, Iowa, a supporter of the barge industry, conducted the research.

Skip Meisner of the Missouri River Keepers said the study shows that present management of the river has been beneficial to birds. The Missouri River Keepers want the corps to maintain the current river flow plan.

However, Chad Smith, a spokesman for American Rivers in Lincoln, Neb., said the study is not based on sound data.

"That report is contrary to the peer-reviewed science on the Missouri River," Smith said. "Any rational evaluation of the scientific data on the birds and the fish show that they are doing worse than they were in the year 2000."

The U.S. Fish and Wildlife Service in 2000 called for a spring rise and lower summer flows once every three years to mimic natural river flows below Gavins Point Dam, the lowest dam on the river. The more natural flows would help the endangered and threatened birds and fish reproduce, the service said.

While American Rivers supports such a change, Meisner said the proposal could harm the birds.

The corps plans to complete a revision of its master river management manual by March 1.