WASHINGTON - The Army Corps of Engineers said Tuesday it won't change plans to release extra water into the Missouri River this year, despite concerns the spring rise will put Missouri farms and the barge industry at risk.

The agency's final operating plan for the river calls for release of two "spring pulses" of water from upstream reservoirs in March, and again in May, to help revive an endangered fish, the pallid sturgeon.

But the releases will happen only if a lingering drought leaves enough water in the reservoir system. Current forecasts show enough storage capacity for the releases to occur, said Paul Johnston, a spokesman for the corps' northwestern division office in Omaha, Neb.

The two-day pulses are supposed to mimic the historic rise of the river with the melting of mountain snow before dams were built. The increased water is intended to encourage the pallid sturgeon to spawn.

Environmental groups generally support the plan as the best way to protect river wildlife, but Missouri Gov. Matt Blunt has threatened legal action. He calls the science sketchy and says the pulses could flood thousands of acres of farmland along the river.

Sen. Kit Bond, R-Mo., also challenged the practical effects of the plan.

"Not one official has suggested that this will lead to recovery of the species," Bond said.

Sen. Byron Dorgan, D-N.D., said he thinks the corps decision favors downstream states at the expense of upstream states.

"I believe the corps ought to recognize the seriousness of the drought in the upstream states and take steps to retain water in our upstream reservoirs," he said.

The final plan announced Tuesday is almost identical to a proposed plan announced Oct. 24. Since then, corps officials considered hundreds of written comments and heard debate at eight meetings in cities along the nation's longest river, which runs 2,714 miles from Montana to Missouri.

The corps developed the plan under orders from the U.S. Fish and Wildlife Service to protect the pallid sturgeon as required under the Endangered Species Act.

Corps officials have spent more than a decade meeting with farmers, navigation interests, environmental groups and state representatives to balance competing interests along the Missouri River.

Upstream states are concerned the release of water will lower already drought-plagued lakes and damage the valuable fishing industry in Montana, North Dakota and South Dakota.

"Although they are clearly trying, this plan still gives upstream states like Montana the short end of the stick," said Sen. Max Baucus, D-Mont. "We need to share the pain more during drought years. This plan doesn't go far enough. It still gives preference to the barge industry."

Barge companies complain that the spring rise limits upstream water available later in the fall, when drought conditions can make the river unnavigable. Last year, the corps cut the navigation season on the river to 48 days - the shortest season on record.

Missouri officials grew concerned in December, when the U.S. Department of Agriculture's Risk Management Agency said farmers who experience crop damage as a result of intentional flooding by the federal government would not be eligible to make federal crop insurance claims.

Reps. Ike Skelton, D-Mo., and Kenny Hulshof, R-Mo., said they are working to find a legislative solution that would help farmers keep insurance coverage in the event of flooding.

A release won't occur unless the water level in the reservoir system is at least 36.5 million acre feet. If that threshold is not met, the corps will postpone the release until 2007.

Johnston said runoff forecasts predict 36.6 million acre feet of water by March 1.