It would cost $283 million to $752 million to build a pipeline to move vast amounts of water across the Continental Divide from the Green River to the North Platte River Basin, state water officials say.

Those are preliminary numbers from a study done by the Wyoming Water Development Commission staff. Commission Director Mike Besson said that expense, coupled with political and environmental hurdles, likely means such a project won't happen for some time, if at all.

"Eventually, maybe someday, there will be some interest and willingness to fund it," he said Thursday. "Right now, it may be premature."

The most recent study of trans-basin diversion was started two years ago to determine if there might be a practical way to take water from a basin where there's a surplus - Green River - to one where water is in short supply - North Platte. Wyoming has rights to 833,000 acre feet annually in the Green River Basin, but 221,300 acre feet goes unclaimed.

"Our job is to take water from places with an adequate supply and move it to places where it is needed," Besson said.

Such a project could aid growth in Cheyenne, Casper and Laramie while protecting irrigators' water rights, he said. But the idea is opposed by environmentalists and southwest Wyoming residents.

The study looked at a 54-inch steel pipeline that would carry 50,000 acre feet of water a year. An acre foot is the amount of water needed to cover an acre 1 foot deep.

The commission staff examined six possible pipeline routes. The least expensive route would be from Fontenelle Reservoir to the Sweetwater River, which empties into Pathfinder Reservoir from the west. The most expensive would be to link Flaming Gorge Reservoir with Seminoe Reservoir.

Besson said the most politically feasible routes would pipe water from the Flaming Gorge area. That would put the pipeline downstream of Wyoming irrigators and towns.

The diverted water would probably cost $140 to $200 per acre foot. Besson said industries and municipalities might be able to afford that, but not irrigators.

"This would be keyed more on if there's a big industrial need," he said. "There might be a partner there someday. But I think it's years away."

Besson said he launched the study after learning of a proposal in Utah to pipe water from southwestern Wyoming's Fontenelle Reservoir to the Wasatch Front. He contends that the water would be better used to bolster the North Platte River.

"I just wanted to send the message that we do need this water here in Wyoming," he said.

At the same time, he recognizes "there are a lot of politics and a lot of tough issues surrounding this."

Gov. Dave Freudenthal opposes the project. Other opponents include Janet Hartford, executive director of the Green River Chamber of Commerce, who said her area depends on the river for tourism, agriculture and business.

If water were diverted, it could stifle growth in southwestern Wyoming, she said.

"When we're recruiting businesses or when a business is looking to move here, they ask us, 'How much water do you have, and how near is it?"' she said. "If we're losing water, we're losing recreational opportunities, and we're losing fish habitat. We're also losing our ability to do business recruitment and expansion."

Erik Molvar, a biologist with the Laramie-based Biodiversity Alliance, said diverting water could harm four endangered fish species in the Colorado River.

"It's always a bad idea to take water from a desert watershed," Molvar said. "We need to look at better ways of supplying our water needs. Destroying our rivers isn't worth the cost."

Besson said the study of a trans-basin pipeline "starts framing other options" for dealing with water demand in the North Platte basin.

"These projects are so extremely expensive, it kind of districts from its attractiveness," he said. "It's about what you can afford to do. This could get us looking at other things - conservation, groundwater development. What can be done in the basin without going to this type of initial investment?"

The commission is also looking at the possibility of expanding water storage in the Green River Basin.

What happens next with the trans-basin pipeline idea? Besson said it would likely take a proposal from a public entity - or a push by state elected officials - to take the concept to the next level of study.

From the perspective of the Water Development Commission - which recommends water projects to the Legislature - "we're more interested in seeing what can be done in the (North Platte) basin first," he said.