If New Year’s Day had happened last week, the Central Arizona Project would have suffered the first water shortage in its 35-year history.

That’s because Lake Mead — where CAP water is stored at the Nevada border — dropped below 1,075 feet elevation late Tuesday, and stayed that way off and on the rest of the week.

That’s the level at which the federal government is legally required to declare a shortage on the Colorado River, curtailing deliveries to Arizona farmers including some in northern Pima County.

But because that requirement doesn’t kick in until the lake lies below 1,075 feet on any January 1st, its level is mainly symbolically important right now, say a leading water researcher and environmentalists.

The lake is expected to rise later this year, due in part to unusual and unexpected heavy rains that fell upstream in Colorado in May and early June. By Jan. 1, it’s supposed to top 1,083 feet. The U.S. Bureau of Reclamation doesn’t predict a shortage until at least Jan. 1, 2017 if not later.

But because most water observers still think the lake’s level is still very vulnerable to drought and overuse of water, they generally agree that the lake dropping below 1,075 feet even now is significant.

“We’ve got problems on the river. There will continue to be problems, certainly as long as the drought continues,” said Sharon Megdal, a CAP board member and director of UA’s Water Resources Research Center. “My point and I think this is what most people say, is that at best we can breathe a temporary sigh of relief.”

“No shortage in 2016 means we’re putting it off until the future,” Megdal said.

Even a couple of wet years due to the ongoing El Niño weather phenomenon won’t correct the problem of “bad math” that led seven Western states to allocate more river water to themselves than actually exists, added Joan Clayburgh, a spokeswoman for the conservation group Western Resource Advocates. That occurred back in 1922 when they drew up the Colorado River Compact.

“A few good wet years might slow it down but it’s inevitable. It’s more like a warning light,” said Clayburgh of the lake’s level. “If it’s not 2017, it will be 2018.”

Lake Mead dipped to 1,074.98 feet at 11 p.m. on June 23. Its level bobbed back and forth between just below 1,075 feet and just above it through the next afternoon. Late Sunday afternoon, the lake level remained below 1,075 feet.

All year, and on and off since October 2010, the lake has been flirting with record low levels. Its levels last week were the lowest since the lake was filling in the middle to late 1930s.

A lot of people have pointed out that the first shortages will be limited to farmers and programs that recharge CAP water into the ground to store for future, deeper shortages, Megdal said. Those programs include the state-run Arizona Water-Bank and the three-county Central Arizona Groundwater Replenishment District.

But even the early shortages will raise the cost of CAP water to urban customers, reduce power output from Hoover Dam and make Mead less accessible to recreation, she said.

Clayburgh and other environmentalists used Mead’s current low level to reiterate their continued push for more water conservation.

“There’s been all kinds of innovations and examples of conservation in various cities, and we need to see these examples replicated across the region,” she said. “They don’t need to be outrageously ambitious. One percent per year of reduced water use, per person, would make huge strides.”

Contact reporter Tony Davis at tdavis@tucson.com or 806-7746. On Twitter: tonydavis987.