SPOKANE, Wash. » The U.S. Interior Department said Tuesday it doesn’t want federal irrigation water being used to grow marijuana in Washington, Colorado or anywhere else.

But the practical effects of the policy are limited: The Bureau of Reclamation said only that it would refer any violations to the Justice Department, and it seems unlikely that the Justice Department would target irrigation districts for supplying the water when it’s not going after the people who are actually growing the pot.

"We’re not an investigative agency. We’re an agency that provides water to irrigation districts," said Dan DuBray, a spokesman for the Bureau of Reclamation in Washington, D.C. "The limit of our proactive stance is that if asked, we’re not approving it, and if we become aware of it, we report it."

Furthermore, it’s not clear the policy will apply at all in Colorado. The bureau left a big exception: If federally provided water is mixed with local water — in a reservoir, say — then it can be used in pot grows. In Colorado, many if not all water districts do "commingle" water in that manner. At least some do so in Washington, as well.

The question of whether federal water can be used to grow marijuana is the latest iteration of a messy conflict posed by the recent legalization of recreational marijuana in Washington and Colorado.

The DOJ announced last summer that even though marijuana remains illegal under federal law, it wouldn’t sue to stop the states from licensing pot growers, processors and sellers as long as those operations are well regulated. But issues keep arising. It took a year for the FBI to agree to conduct background checks on pot-business applicants in Washington state, for example.

"The Department of Justice will continue to enforce the Controlled Substances Act and will focus federal resources on the most significant threats to our communities," the DOJ said in response to an inquiry about its intentions with regard to violations of Reclamation’s new policy.

Reclamation provides irrigation water in 17 states, mostly in the West. The bureau operates giant dams and vast networks of canals that provide water through much of the arid West. That includes the mammoth Columbia Basin Project in Eastern Washington, which provides water for more than 600,000 acres of apples, potatoes, wine grapes and other crops.

Local water districts had asked the agency to set a policy on use of federal water to grow marijuana, DuBray said.

Historically, those districts have never regulated what crops are grown with the water they provide, and they’re not inclined to start.

"Our underlying goal is to continue delivering water to our water users and leave policing to those with police powers," said Tom Myrum, executive director of the Washington State Water Resources Association.

Brian Werner echoed that. He’s the spokesman for Northern Water, a public agency that works with Reclamation to provide water to more than 640,000 acres of irrigated farm and ranch land and about 860,000 people in northeastern Colorado.

"We’re not in the enforcement business, and we don’t plan on getting in the enforcement business," he said.

It’s unknown how many legal marijuana growers in Washington are using or planned to use water from the Bureau of Reclamation. Washington’s Liquor Control Board, which is in charge of regulating pot, doesn’t track that, said spokesman Brian Smith.

One licensed grower in Eastern Washington said her farm is using federal water; she spoke on the condition of anonymity to avoid drawing attention to that and risking having her water shut off.

She noted that other options exist. Under Washington law, growers in many parts of the state can use well water as long as they draw less than 5,000 gallons per day. But sinking a well would be at least a $10,000 expense she and her partners hadn’t planned for, she said.

"Will they come and shut off the water?" she asked. "Or will they just send a note to the Justice Department and say, ‘Hey, look over here’? That’s the question."

All of Colorado’s 980 licensed pot growers operate in greenhouses that use water from local water districts, which can include Reclamation water. Colorado does not permit outdoor marijuana cultivation, but pot growers there have been using federal water in licensed, indoor medical marijuana grows since 2010.

Three members of Congress from western states criticized the Reclamation Bureau decision. U.S. Reps. Jared Polis, D-Colo., Earl Blumenauer, D-Ore., and Suzan DelBene, D-Wash., said it was one more action by the federal government that confused the marijuana issue.

"Today’s decision again brings federal, state, and local law into conflict in a way that creates uncertainty among residents of states that have approved the use of marijuana," Blumenauer said. "The administration needs to give clear marching orders to the various agencies and for them to get in step to avoid problems like this in the future."

Johnson reported from Seattle. Kristen Wyatt contributed from Denver.