BISMARCK, N.D. — A United States federal judge has halted pipeline construction on a long-delayed project to supply growing northwestern North Dakota communities with water from the Missouri River, prompting project leaders to begin exploring another potential water source.

U.S. District Judge Rosemary Collyer in Washington, D.C., ruled March 1 that all pipeline construction on the Northwest Area Water Supply project must stop pending the outcome of a federal study of its potential impact on Canada and Missouri. The project manager expects the study to be finished next year.

"The court's duty ... is to ensure that a no-go option receives the complete consideration it requires without undue influence from North Dakota's impatience," Collyer said in her ruling dated March 1.

Missouri and Manitoba, which borders North Dakota, are suing to stop the project, which Congress authorized in 1986.

Manitoba sued in 2002, when construction began, over concerns about the pipeline's possible transfer of harmful bacteria or other agents from the Missouri River Basin to the Hudson Bay Basin.

Missouri, which sued in 2009, fears the pipeline would deplete one of its key sources of water. The Missouri River provides water to three million Missouri residents and is vital to the state's shipping and agriculture industries.

"Missouri's concern over cumulative depletions is heightened by this year's severe drought in the Missouri River basin and the likelihood of future years of drought," Missouri Attorney General Chris Koster said in a January court filing.

When Manitoba sued, Collyer ordered another, more thorough, environmental review of the project, which led to the creation of a water treatment plan approved by the federal Bureau of Reclamation in 2009.

In the meantime, the judge allowed construction to continue as long as it was not related to water treatment.

Missouri then sued, saying the environmental study didn't consider the project's impact on downstream Missouri River water supplies.

Collyer, who combined the two lawsuits, last week ordered all pipeline construction to stop until the Bureau of Reclamation can study all aspects of the project's potential impact. She only allowed upgrades being made to Minot's water treatment plant tocontinue.

Tim Freije, who is overseeing the project for North Dakota's State Water Commission, said state and federal officials have begun exploring using aquifers fed by the Souris River as the project's potential water source, even though the state would rather tap the Missouri River because it is more plentiful and has better quality water.

"We basically just decided we would go back to Square 1, look at all scenarios," he said.

Freije acknowledged that using the aquifers might be a way to satisfy both the concerns of Missouri and those of Manitoba, since the Missouri River would not be tapped and the Souris River already is a part of the Hudson Bay watershed.

However, "there are a lot more unknowns with that option than there is with the Missouri," Freije said.

Abandoning the Missouri River option also would mean that about $26 million worth of pipeline that has been installed between Minot and the river would be useless.

Collyer in 2010 barred the state from doing design work on a water intake connecting the river and the pipeline.

About $110 million of local, state and federal money has been spent on the project, and it could cost two or three times that to complete it, Freije said.

About 240 miles of the planned 300 miles of pipeline has been laid and the project already is supplying 17,000 to 20,000 people with water, though it is treated groundwater from the Minot plant and not Missouri River water.

Once finished, the project could serve as many as 81,000 people, according to Freije.

Freije said he doesn't expect the environmental study to be finished for another year, at which time the court battle would likely continue.

"Ultimately, we'll do what we have to do because that area (northwest North Dakota) is growing and the existing water resources are deficient," Freije said. "We're just trying to meet the needs of our citizens."