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.

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 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.

“That report is contrary to the peer-reviewed science on the Missouri River,” said Chad Smith, a spokesman for American Rivers in Lincoln, Neb. “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 corps plans to revise its master river management manual by March 1.