FRESNO  (AP) — Officials said Tuesday that, for the first time in decades, they plan to tap water stored behind a dam east of Fresno, as they try to help California farmers through the ongoing drought.

Pablo Arroyave of the U.S. Bureau of Reclamation said in a conference call with reporters that low water levels in the Sacramento-San Joaquin Delta have forced officials to turn to Friant Dam on the San Joaquin River. The dam forms the Millerton Lake reservoir.

Millerton Lake water is needed to meet the bureau’s contractual water obligations to the San Joaquin River Exchange Contractors Water Authority, which holds senior water rights. The exchange provides irrigation water to about 240,000 acres of farmland between Patterson and Mendota.

The bureau has relied solely on Sacramento-San Joaquin Delta to meet the exchange’s needs. The additional water will begin to flow through the Friant Dam on Thursday, Arroyave said.

“We continue to be in a very serious drought with very serious impacts,” Arroyave said.

In 1939, the federal government reached an agreement with the exchange to take its water from the Delta rather than the San Joaquin River, unless the Delta couldn’t meet the need. In the drought, the Delta cannot provide enough water, marking a first since the agreement was struck.

Steve Chedester of the exchange said that more water is always good news for the 2,300 farms he serves. But he noted that the government says it will provide an increased amount of water through October. He worries about November and December, adding that the bureau says it remains committed to finding supplies for the exchange then, as well.

“We are committed to helping the bureau try to find that water,” he said. “In our perspective, it needs to be the full amount for the full year.”

Aside from these changes, the allotment of irrigation water to many Central Valley farmers who aren’t considered senior rights holders is expected to remain at zero for the rest of the year, officials said.

The bureau also announced that it is increasing from 40 percent to 65 percent of normal the amount of water to wildlife refuges south of the Delta.

Mike Lynes of Audubon California welcomed the additional water to help migratory birds that depend on the Central Valley wetlands for their survival.

“It’s hard times for everybody — for farmers, for water districts, folks in the city and for wildlife,” he said. “We’re all in this together.”