The federal government tightened the screws on the overtaxed Colorado River Friday, announcing that it will cut water releases from Lake Powell to Lake Mead for the first time ever starting in October.

The U.S. Bureau of Reclamation also warned that odds are now 51 percent that shortages will occur in 2016 for the Central Arizona Project and other Lower Colorado River Basin water users.

That follows a record-setting 14 years of drought on the river, with the last two years being particularly dry.

The odds of a CAP shortage in 2015, previously considered unthinkable, are now 2 percent, the bureau said. The shortage risk hits 59 percent starting in 2017. Those odds continue at roughly 60 percent for the next decade, bureau figures show.

“Is it a time to panic? No. But it’s absolutely a time to plan,” said Gary Wockner, campaign coordinator of the Denver-based Save the Colorado, an environmental group.

News of the reduced releases triggered warnings from environmentalists that a new era is beginning of a water-short river, which now serves about 40 million people and irrigates 5.5 million acres of farmland.

These conditions require major changes in management and a much greater emphasis on water conservation, environmentalists said.

CAP officials took the news more in stride, saying they’d expected something like this to happen. They say that while management changes are needed, the seven river-basin states including Arizona are already working on how to adapt river management to a more arid West due to climate change and drought, and that measures to augment the river’s supplies are also needed.

Central Arizona Project officials say the first shortages would slash the project’s supply by 20 percent, affecting farmers and those such as the Arizona Water Bank, a state agency, that buy and recharge river water for future use.

Shortages severe enough to affect Tucson, which relies more than ever on CAP for drinking water, and other urban customers are still 10 to 15 years away, said David Modeer, CAP’s general manager.

The Bureau of Reclamation’s decision to cut releases into Lake Mead by about 9 percent was spurred most immediately by a particularly parched July. That month, water flows from the river and its tributaries into Lake Powell at the Utah border were only 13 percent of normal.

That’s barely half what authorities had expected for July. Until that happened, bureau officials were expecting that the lake would get just enough water to avoid curtailing releases to Lake Mead.

For the entire April-July, spring-summer runoff season, flows into Lake Powell were 36 percent of normal, on top of 29 percent of the normal runoff in the same period of 2012.

As a result of these dry conditions, Lake Powell will now release 7.48 million acre-feet of water to Lake Mead for the October 2013-September 2014 period. That compares to historical releases of 8.23 million acre-feet. An acre-foot will supply two to three families with a year’s worth of water.

“I don’t think it’s any surprise. We’ve been expecting this, given below-normal flows for two years,” CAP’s Modeer said Friday.

He noted that back in 2007, the seven basin states reached a river-management agreement that set triggers for cutbacks in releases to Lake Mead that are based on how much water is available in Powell. Given those agreements and the continued drought, “we fully expected these levels will occur.”

But in the Las Vegas area, which depends far more on river water than Arizona, the regional water chief, Pat Mulroy, had already asked for the Obama administration to declare the river a disaster area, making the region eligible for federal aid.

In a recent interview with the Las Vegas Review-Journal, Mulroy compared this drought to Hurricane Sandy on the East Coast last year, saying, “Does not a drought rise to the same level as a storm? The potential damage is just as bad.”

Bureau officials said Friday that they typically don’t reply to other officials’ comments. But they said that while they believe drought and climate change are affecting water supplies, “the system is quite variable and we could see a change in supply with another good year like 2011,” in which the river received flows far above normal.

In Colorado, Eric Kuhn, general manager of the Colorado River District, warned in a memo last month that the river’s low flows could reduce Lake Powell’s elevation enough that the water would be too low by 2015 to generate power in the Glen Canyon Dam’s turbines.

The federal reclamation agency’s monthly two-year river forecast, released Friday, isn’t anywhere near that dire. But bureau officials did say that Glen Canyon’s power production would be reduced 8 percent in 2014, although Hoover Dam’s power production won’t be cut.

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Today, Lake Mead at the Nevada border is 47 percent full, and Lake Powell is 45 percent full.

Combined, Powell and Mead are projected to be at their lowest percentage of capacity this fall since Lake Powell filled back in 1980, at a combined 45 percent. The previous low was 46 percent in 2014.

For next year, Lake Powell is expected to continue to receive below-normal flows, partly because soil in the river’s Upper Basin is so dry that much precipitation will soak into it rather than running into streams.

“Today was the first step in public recognition that we are in a new paradigm,” said Wockner, of the Save the Colorado group. “The important thing to remember is that there is no prediction that there is going to be any more water.”

He and a second Denver-based river conservation group, Protect the Flows, asserted that the cheapest and fastest solutions to the river’s woes are dramatic increases in water conservation and efficiency measures.

CAP’s Modeer said river basin states are likely to take extraordinary steps to ensure adequate water supplies, including fallowing of farmland in some states and cutting back some urban water use.

But he warned that conservation alone won’t do the job, and some kind of augmentation program, possibly including salt-water desalination, must be considered.

The states are exploring a number of ideas for water, but “I don’t have a time frame” for when anything might be adopted, he said.

The high-water mark for Lake Mead is clearly visible at Hoover Dam. In the Las Vegas area, which depends far more on river water than Arizona, regional water chief Pat Mulroy has asked for the Obama administration to declare the Colorado River a disaster area. 

This April 16 photo shows the “bathtub ring,” Lake Mead’s high-water mark, near Hoover Dam. The U.S. Bureau of Reclamation said Friday that it will cut water releases from Lake Powell to Lake Mead for the first time ever starting in October.

Contact reporter Tony Davis at tdavis@azstarnet.com or 806-7746.