In a clear indicator that California is descending into a fourth year of drought, the federal government on Friday announced that the Central Valley Project — California’s largest water delivery system — will provide no water again this year to most Central Valley farmers and only 25 percent of the contracted amount to urban areas such as Santa Clara, Alameda and Contra Costa counties.

The announcement from the Bureau of Reclamation means that farmers in California’s main agricultural region will fallow hundreds of thousands of acres, and heavily pump already depleted wells, perhaps faster than last year.

It also increases the likelihood of stricter conservation rules — including fines for excessive water use — this summer for millions of residents who receive water from the Santa Clara Valley Water District, the East Bay Municipal Utility District and the Contra Costa Water District, all of whom draw a portion of their supply from the Central Valley Project.

“Today’s picture is not a pretty one,” said David Murillo, regional director for the Bureau of Reclamation. “Based on all indicators, we are looking at a fourth year of drought.”

The Central Valley Project was built starting in the 1930s. It moves water from Shasta Lake near Redding all the way to Bakersfield through a series of 20 dams, 500 miles of canals and huge pumps. In most years, the project provides nearly 90 percent of its water to farms. In dry years, cities receive priority over most farmers. Farmers, however, with the oldest claims to water could receive up to 75 percent of their contracted amounts this year.

Meanwhile, urban water providers said Friday’s news means they will scramble to increase conservation, buy water from the few willing sellers, and will rely on heavier groundwater pumping to get through the year.

Most of California’s major cities have so far gotten by with only voluntary conservation rules, with no fines or water cops. That may well change now.

“Unless it pours rain in the next two months, we’re facing a long, dry, tough summer,” said Abby Figueroa, a spokeswoman for the EBMUD, which serves 1.3 million people in Alameda and Contra Costa counties.

Figueroa said the district’s board will meet in April to discuss putting in place penalties for excessive water use, and mandatory limits on when people can water lawns. Some cities, like Morgan Hill, already limit lawn watering to only one day a week.

Customers in EBMUD and the Santa Clara Valley Water District cut use 13 percent last year from the prior year. Not bad, but below Gov. Jerry Brown’s request for 20 percent.

On March 24, the Santa Clara Valley Water District will discuss tougher conservation measures, which could include asking South Bay cities to strictly limit lawn watering and, for the first time during this drought, issue fines for violators. They also will consider further ramping up rebates for people who remove lawns and buy water-efficient appliances. To make up for the lack of rain, the district has been heavily pumping groundwater, taking the water table under San Jose down 60 feet over the past three years.

“We’re going to have to do more belt-tightening,” said Garth Hall, district deputy operating officer. “I don’t know how far each city will go. It’s going to vary across the landscape.”

At the Contra Costa Water District, the board in April will consider tightening a rule that doubles the cost of water for households that use more than 1,000 gallons a day — about triple the area average.

Residents in San Francisco, the Peninsula and South Bay who receive Hetch Hetchy water are not affected by Friday’s announcement.

The last three years have been the driest three-year period in California history back to the Gold Rush in 1850. Although Northern California received several strong storms in December and February — and is expecting light rain this weekend — those storms have not built up the state’s critical Sierra Nevada snowpack, which stood at 19 percent of normal on Friday. That’s because they were warm storms, and record hot temperatures in January and February have melted much of the snow.

“We’re flirting with the lowest snowpack on record,” said Frank Gehrke, chief of the state’s snow survey program.

Farm groups said Friday the news means major economic pain in the San Joaquin Valley and other agricultural regions, many of which received no federal water last year.

“As rural Californians face an uncertain future, their communities will continue to struggle with mounting unemployment and economic hardship,” said Mike Wade, executive director of the California Farm Water Coalition.

Wade called the announcement “a tragic repeat of last year,” and said more jobs will be lost and land fallowed.

Last year, 428,000 acres, or 5 percent of the state’s cropland, was left unplanted because of the drought, and 17,100 jobs — about 4 percent of all state farm employment — were lost.

Wade called on the federal government to relax regulations to protect salmon, smelt and other endangered fish to allow more water to be pumped out of the Sacramento-San Joaquin River Delta, something environmental and fishing groups oppose.

“Coming on the heels of the driest three-year period in California’s history, it’s not surprising that allocations are low across the state,” said Doug Obegi, an attorney with the Natural Resources Defense Council in San Francisco.

Pumping even more water out of the Delta will increase salinity and harm drinking water quality for 25 million California residents, Obegi said, noting there already have been huge salmon die-offs due to water cutbacks and increased river temperatures.

“Waiving environmental laws won’t make it rain,” he said.

Staff writer Kim Smuga-Otto contributed to this report. Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/paulrogerssjmn.