After expressing their frustration privately for weeks, negotiators for four Colorado River Basin states sent a strongly worded letter to Arizona water managers on Friday, singling out the actions of one state agency as “threaten[ing] the water supply for nearly 40 million people.”

In the letter, the Upper Colorado River Commission said those actions could threaten efforts to conserve water and prevent Lake Mead from going into shortage for as long as possible. It could, they wrote, also undermine a decade of broader collaboration intended to avoid costly litigation between Colorado River users.

In a second letter released on Monday, Denver Water told the Arizona water agency — the Central Arizona Project — that it is prepared to pull conservation funding because CAP’s actions “severely compromise the trust and cooperation that has allowed us to develop [the program].”

The mounting pressure on CAP, which is operated by the Central Arizona Water Conservation District (CAWCD), comes as the agency is engaged in a fight within Arizona over how to manage the state’s Colorado River water. At issue is whether the Central Arizona Project, which delivers water to Tucson and Phoenix, is gaming a set of guidelines intended to balance the river’s reservoirs during times of drought. The Arizona Department of Water Resources, an arm of the governor’s office, has criticized CAP’s strategy for months and now other Colorado River users are piling on, warning the agency to stop before it jeopardizes delicate negotiations over drought planning.

In response to the letters on Monday, Arizona's top water official doubled down on his criticism. Tom Buschatzke, who directs the Arizona Department of Water Resources, said he shared some concerns in the letter and agreed CAP was manipulating the system to get more water from the Upper Basin. 

“I have huge concerns that the unilateral actions of CAWCD are threatening the regional and binational [drought] plans… that will benefit and protect Lake Mead,” Buschatzke said on Monday in response to the two letters.

In a statement, CAP said it was “surprised and disappointed to have received a letter from the Upper Colorado River Commission questioning CAWCD’s intentions in leaving water in Lake Mead. We have been reaching out to our partners in the Upper Basin, hoping to clarify apparent misunderstandings, and to facilitate in-person, collaborative discussions aimed at finding solutions that will benefit the communities and environment served by this mighty river.”

What’s going on here

The Colorado River is split into an upper and a lower basin with two main reservoirs in each division — Lake Powell and Lake Mead. Under the 1922 Colorado River Compact, the Upper Basin states of Colorado, New Mexico, Wyoming and Utah are obligated to release a certain amount of Lake Powell water for the Lower Basin states of Arizona, California and Nevada.

On top of that, the Upper Basin has agreed, in recent years, to send “bonus water” to Lake Mead if it is at a low elevation relative to Lake Powell. The dispute with CAP is about the “bonus water.” Recently, CAP has advocated in presentations for keeping Lake Mead at a “sweet spot” — high enough to avoid a shortage but low enough to get “extra water” from Lake Powell.

This creates a political issue for the Upper Basin. It wants to store water in Lake Powell and boost the reservoir's elevations. That way it can ensure full deliveries to the Lower Basin in dry years and continue producing hydropower.

CAP is undermining efforts to keep water in Lake Powell, the letters argue, by adjusting how it orders water from Lake Mead (CAP's general manager Ted Cooke defended this practice on Twitter last week as placing its "water order wisely").

The letter signed by representatives for all the Upper Basin states calls CAP's action a “strategy to intentionally maximize demands within the Central Arizona Project to induce larger than normal releases from Lake Powell.” The “goal,” they wrote on Friday, “appears to be to delay agreement on drought plans in order to take advantage of what it terms the ‘sweet spot.’”

Denver Water called it “unacceptable.” The municipal agency said that it would cancel funding for a Colorado River conservation program in the Upper Basin unless CAP “is able to verifiably establish it has ceased all actions to manipulate demands and is fully participating in aggressive conservation.”

In recent months, Cooke has defended CAP's decisions. CAP's supporters see the actions as a water agency acting in its own interests. Cooke argued that it would be counterproductive to store more water in Lake Mead because that could boost its elevation so much that the Lower Basin would forgo any "bonus water." Arizona would take the steepest cuts during a shortage. He has said the best thing to do is to get as much water from Powell as the current rules allow and use it to mitigate a shortage.

Why this matters:

• The drought plan: CAP’s position could make it even more difficult, the Upper Basin negotiators argued, to agree on a basin-wide drought plan. Both basins have been working to finalize drought plans by August — a challenging deadline at this point. One component of the Upper Basin plan was to leave more water in Lake Powell through the type of conservation Denver Water was funding. But water users in the Upper Basin are unlikely to fund an expensive program like that unless they are assured the water will stay in Lake Powell. As Denver Water put it in on Monday, “CAWCD’s manipulation of demands in order to take advantage of the supposed ‘sweet spot’ in Lake Powell water releases undermines this purpose, and is unacceptable.”

• Gaming itself? Upper Basin negotiators argued that CAP’s strategy could make a shortage in Lake Mead more likely, especially after a dry winter. The rules, they said, are written so that “with continuing poor hydrology, attempts to maximize demands to increase releases from Lake Powell could ultimately accelerate lower reservoir conditions... and cause shortages in Lake Mead.”

• A departure from the norm: John Fleck, a Colorado River expert who first reported the Upper Basin letter, wrote that the language was “striking in the normally staid interstate diplomacy of Colorado River interstate water management.” That might be by design. The letter is itself a response to what the Upper Basin sees as a departure from what it called “interstate comity.” 

“What they are doing is rolling the dice,” Denver Water CEO James Lochhead said. “They feel like they are playing with house money but they are playing with everybody else’s water supply.”

How this ends:

In its statement, CAP said that it hoped to engage in “collaborative discussions."

“I do expect that this can be a catalyst to change,” Buschatzke said. “It is pretty much an unprecedented action to send this kind of letter."

If the fight continues, Buschatzke laid out the worst-case scenario, something that all Colorado River users have worked for a decade to avoid — a conflict that could lead to litigation.

“This really threatens to blow up that collaboration and send us back into the days of saber-rattling, confrontation and perhaps litigation,” Buschatzke said.

CAP said that it would be reaching out to its partners. As of Monday afternoon, Lochhead at Denver Water had yet to hear from them, but he said that the Arizona water agency should not be “surprised” by the letters. 

“They forced the issue and somebody had to stand up,” he said.