LOS ANGELES — The snowpack in the Sierra Nevada is the deepest it’s been in decades, but those storms that were a boon for Northern California won’t make much of a dent in the long-term water shortage for the Colorado River Basin — an essential source of supplies for Southern California.

In fact, the recent storms haven’t changed a view shared by many Southern California water managers: Don’t expect lakes Mead and Powell, the nation’s largest reservoirs, to fill up again anytime soon.

“To think that these things would ever refill requires some kind of leap of faith that I, for one, don’t have,” said Brad Udall, a water and climate scientist at Colorado State University.

Lake Mead, located on the Arizona-Nevada border and held back by Hoover Dam, filled in the 1980s and 1990s. In 2000, it was nearly full and lapping at the spillway gates. But the megadrought over the last 23 years — the most severe in centuries — has worsened the water deficit and left Lake Mead about 70% empty.

Upstream, Lake Powell has declined to just 23% of full capacity and is approaching a point where Glen Canyon Dam would no longer generate power.

Even with this winter’s above-average snowpack in the Rocky Mountains, water officials and scientists say everyone in the Colorado River Basin will need to plan for low reservoir levels for years to come. And some say they think the river’s major reservoirs probably won’t refill in our lifetimes.

“They’re not going to refill. The only reason they filled the first time is because there wasn’t demand for the water. In the 1950s, ’60s, ’70s and ’80s, there was no Central Arizona Project, there was no Southern Nevada Water Authority, there was not nearly as much use in the Upper (Colorado River) Basin,” said Bill Hasencamp, manager of Colorado River resources for the Metropolitan Water District of Southern California. “So the water use was low. So that filled up storage.”

Demand for Colorado River water picked up in the late 1990s and early 2000s. The Central Arizona Project, a 336-mile-long water delivery system, brings water from the Colorado River to Arizona’s most populous counties and wasn’t completed until the 1990s. The Southern Nevada Water Authority was created in 1991.

Arizona began starting to take its full apportionment of river water in the late 1990s, and Nevada in the early 2000s. California continues using the single largest share of the river.

“Now the water use is maxed out. Every state is taking too much, and we have to cut back. And so there’s just not enough. You would need wet year after wet year, after wet year after wet year, after wet year. Even then, because the demand is so high, it still wouldn’t fill,” Hasencamp said in an interview.

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