SPOKANE, Wash. (AP) — 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 remain unclear: 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.”

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 use 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, and the prohibition against using that water to grow pot applies to all of them. 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.

It’s unclear 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, has no way to 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 fact 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.”

Meanwhile, all of Colorado’s 980 licensed pot growers operate in greenhouses that use water from local water districts, which include Reclamation water.

Colorado does not permit outdoor marijuana cultivation, but pot growers there have been using federal water in licensed indoor grows since 2010.

“We’re used to this kind of treatment, the federal government looking for one obstacle after another to place hurdles before this industry,” said Elan Nelson, business consultant for Medicine Man dispensary in Denver. “We’ll just have to find a way to deal with it and move on.”

“Pretty soon it’s going to be air,” Nelson said. “They’re going to say you can’t use the air because it belongs to the federal government. It’s just ridiculous.”

The Reclamation Bureau decision comes as marijuana is gaining more public and governmental acceptance.

For instance, a poll released last month found that three-fourths of Americans say it’s inevitable that marijuana will be legal for recreational use across the nation, whether they support such policies or not. The Pew Research Center survey also showed increased support for ending mandatory minimum prison sentences for non-violent drug offenders.

Since California became the first state to legalize medical marijuana in 1996, 20 others and the District of Columbia have followed suit. More than a dozen state legislatures considered legalization measures this year.

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Johnson reported from Seattle. Kristen Wyatt contributed from Denver.