3:47 a.m. - OMAHA, Neb. (AP) -- Environmentalists, farmers, tribal leaders and others are gathering here for a three-day meeting on the spring rise of the Missouri River.

The meetings, to start Tuesday, will be the third such gathering to discuss the spring rise, which involves water being released into the river from Gavins Point Dam in South Dakota to provide a spawning cue for the endangered pallid sturgeon. An earlier meeting was held in Bismarck.

In 2003, the U.S. Fish and Wildlife Service ordered the Army Corps of Engineers -- which manages the river -- to come up with a spring rise plan by next year.

"The rise is going to happen," said Paul Johnston, a spokesman for the Corps of Engineers on Monday. "The meetings are to define when and how."

Johnston said the corps has a default plan for a spring rise that will be enacted for 2006 if the meetings fail to yield another option.

Chad Smith of the environmental group American Rivers has attended the two previous meetings and said he is confident a reasonable spring rise plan can be developed at the meetings in Omaha.

"The bottom line is, it is something that has to be done," Smith said. "I remain very optimistic that we can come to a consensus recommendation and that we can use this as a jumping-off point for the long term."

Pallid sturgeon numbers have been decreasing since the corps straightened and dammed the river about 50 years ago. Environmentalist groups such as American Rivers have argued that a spring rise, which occurred naturally before the river was straightened, will help rebuild the sturgeon population.

A potential spring rise creates questions up and down the 2,341-mile river.

In northern river states, one fear is that releasing water from reservoirs will weaken the water supply, which is problematic in the face of drought, Johnston said.

Downstream, he said, some worry that the released water will increase the chances of floods.

Smith said such factors are being taken into consideration.