With a third year of drought shrinking the creeks that cascade down the eastern Sierra Nevada, the level of Mono Lake has fallen so low it has triggered a 72% reduction in the amount of water Los Angeles can divert from area streams this year.

On April 1, Mono Lake's level measured just under 6,380 feet above sea level—about 1 inch below a threshold set in the Los Angeles Department of Water and Power's licenses for diverting alpine runoff from streams that feed the lake east of Yosemite National Park.

The measurement, taken at the start of a new runoff year, triggered a requirement that the DWP reduce its annual water exports from 16,000 acre-feet, which is enough to supply 192,000 residents, to 4,500 acre-feet, enough to serve 54,000 residents.

The last time Mono Lake fell below the same threshold was from 2015 to 2017, in the final years of California's last severe drought. The level is measured by gauges along a crusty stretch of shoreline next to the town of Lee Vining.

The hypersaline high-desert lake, famous for its towering, craggy tufa formations, has been at the center of long-running disputes over the city's diversions of water from the lake's feeder streams. The State Water Resources Control Board established limits on diversions in 1994 to resolve a fight between environmentalists and the city 350 miles south.

Since then, the DWP says its water diversions from the Mono Basin have been reduced by 80% and it has taken an "environmentally focused approach" to water exports that has included investing in restoration projects. The department says these projects have been successful in improving the ecological health of fish populations and riparian habitats that are vital for birds.

But conservationists remain concerned about the environmental effects of decades of water diversions, especially given the current extreme drought and the worsening effects of global warming.

"Twenty-eight April Firsts have passed since the state water board decision," said Geoffrey McQuilkin, executive director of the Mono Lake Committee, a nonprofit focused on protecting the ecosystem, "yet Mono Lake remains chronically and artificially low."

McQuilkin said Los Angeles has achieved remarkable success in conserving water and developing sustainable water supplies for its roughly 4 million ratepayers, but the city has yet to "repair the damage done by decades of excessive water diversions at Mono Lake in the past."

Adam Perez, the DWP's aqueduct manager, said the department is fulfilling its obligations under its license agreement and is committed to protecting the environment and the health of Mono Lake and its feeder streams.

The department's staff in the area includes biologists and hydrologists and other specialists who study the lake's health, monitor stream flows and sediment on stream bottoms, and track fish populations and water sources that support birdlife. Perez said the restoration projects in the Mono Basin have had success in improving the health of streams, riparian vegetation and wildlife habitats.

"We're trying to do our best in balancing the needs of a large city as well as making sure that we can balance the needs and the restoration of Mono Lake as well," Perez said.

After the reductions in water deliveries during the last drought, Mono Lake's level rebounded with wet weather in 2017, then declined over the last three extremely dry years.

The city has infrastructure in place to use water from several streams—Lee Vining Creek, Walker Creek, Parker Creek and Rush Creek—but is currently diverting water from two of them, Rush and Lee Vining creeks, while not using the other two, Perez said.

Over the last runoff year from April through March, the DWP exported 13,800 acre-feet from Mono Basin, less than the permitted 16,000 acre-feet. That amount will now shrink by two-thirds during the next 12 months.

In the nearly three decades since the state's order restricted water diversions, the hydrology in the Eastern Sierra has become more extreme, with wetter wet years, drier dry years and longer droughts, which the DWP says has made efforts to boost the lake's levels more difficult. During the last year of extreme heat and dryness, the department says about 150,000 acre-feet of water evaporated from the lake's surface.

In 1994, the state water board laid out a target of restoring Mono Lake to a level of 6,392 feet, about 12 feet above the current level, to protect the ecosystem, water quality and air quality. At that time, the DWP says officials estimated based on models that the longest period to reach that level would be 38 years, or 2032.

"The longer periods of dry have definitely impacted the ability for the lake to rise as forecasted back in the '90s, when they put these models together," Perez said. And the department says updated models that include the effects of climate change suggest reaching that higher level could take years longer than had been projected.

In the meantime, the Mono Lake shoreline is continuing to retreat, creating a "bathtub ring" of dusty lake bottom. Warmer temperatures, increased turbidity, and reduced flows in the creeks threaten trout populations and riparian vegetation that is home to migrating birds such as yellow warblers and lazuli buntings.

With evaporation outpacing inflows from those streams, a sheet of water less than 4 feet deep and a few hundred yards wide is all that protects tens of thousands of breeding gulls from predatory coyotes.

"The relationship between Los Angeles and Mono Lake remains a work in progress," McQuilkin said, "and the current drought isn't helping."

The DWP says the reductions in water deliveries have left water in the Mono Basin to support its environmental projects.

"The result of our work is significant," the DWP said in an emailed statement. "Mono Lake and its tributaries now offer abundant resources for the unique water birds nesting on shore, and a healthy environment for the plants and fish to thrive."

The department also plans to begin a $50 million project on the spillway of Grant Lake Reservoir on Rush Creek, which it says will increase stream flows in wet years.

If the drought persists through this runoff year, Perez said, the DWP will probably be permitted to export the same limited quantity of water next year. If the lake continues to decline in future years below a lower threshold of 6,377 feet, Perez said, "our exports would be essentially turned off from Mono Basin."

The water from Mono Basin represents a small portion of the water the DWP transports through the Los Angeles Aqueduct.

According to DWP figures, 48% of the city's water between 2016 and 2020 came via the aqueduct from the Eastern Sierra. The city purchased 41% from the Metropolitan Water District of Southern California, including 35% from the Bay Delta and 6% from the Colorado River. The remainder included 9% groundwater and 2% recycled water.

City officials have laid out goals for decreasing L.A.'s reliance on imported water supplies and expanding local supplies, including recycling more wastewater, capturing more storm water and purifying contaminated groundwater so it can be pumped and used. But the DWP says local water supplies cannot entirely replace imported water.

When the department faces cutbacks on the L.A. Aqueduct, the city typically secures water from the Colorado River Aqueduct and the State Water Project to supplement its supplies. But managers of water agencies expect to receive just 5% of their full allocations from the Bay Delta via the State Water Project this year, and the Colorado River is also in a severe shortage, with reservoirs continuing to decline.

Gov. Gavin Newsom has called on Californians to voluntarily reduce water use 15%, and state officials have urged residents to step up conservation efforts.

"Water allocations are extremely difficult for us at this point," Perez said. "I think that right now, everybody from throughout the state of California, throughout the West, is going to be looking at each other and figuring out ways that we can all conserve and do our part, because we are in a tough situation."

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