The Colorado city of Pueblo has informed water managers that it will no longer participate in a conservation program to boost the elevations of Lake Powell and Lake Mead. It is the latest result of an ongoing feud between an Arizona agency and several Colorado River users that say the agency’s actions could threaten a basin-wide conservation program and drought planning.

Pueblo Water’s decision comes after four states and Denver’s municipal water agency accused the Arizona agency — the Central Arizona Water Conservation District — of undermining Lake Powell elevations by manipulating the complicated supply-and-demand rules that govern water orders.

“Given our recent knowledge of the actions taken by [CAWCD] we cannot, in good conscience, participate in the program,” Seth Clayton, Pueblo Water’s executive director, wrote in the letter.

The letter, dated April 18, comes as the Arizona agency is set to meet next week with negotiators for the Upper Basin states of Colorado, New Mexico, Utah and Wyoming. The Colorado River is split into two basins with two main reservoirs. The Upper Basin stores water in Lake Powell and the Lower Basin stores water in Lake Mead, 30 miles outside of Las Vegas.

The Arizona agency at the center of the controversy, CAWCD, has kept quiet in recent days, despite increasing media attention, so as not to affect the outcome of those discussions.

The Lower Basin states of Arizona, California and Nevada are also scheduled to meet on May 2, although that meeting had been scheduled before the letters to CAWCD were reported last week. The commissioner for the Bureau of Reclamation had been invited to that meeting.

The Pueblo letter confirms what Upper Basin water managers feared — that Arizona’s actions would dissuade water users from joining the conservation program. The program, which is in its pilot phase, pays water users to conserve. The hope is that the conserved water, by not leaving the system, will boost the elevation of Lake Powell. The Arizona agency has said it wants to maximize the amount of water it gets from the Upper Basin, which stores water in Lake Powell.

"[Upper Basin water users] do not want to be putting water into Lake Powell if it gets immediately pulled down to feed this policy that the district is trying to advance," said James Eklund, who represents the state of Colorado on the Upper Colorado River Commission.

CAWCD has said its strategy is to help Arizona prepare for shortage, noting that its actions are permissible under current Colorado River rules. In a statement last week, a spokesperson said: “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.”