As California endures its fourth year of a crippling drought, Gov. Jerry Brown announced Wednesday the state’s first mandatory water restrictions, ordering cities and towns to cut water use by 25 percent.

“It’s a different world,” Brown said. “We have to act differently.”

He spoke from a dry patch of grass in the Sierra Nevada near Lake Tahoe, where a melting snowpack would normally provide nearly a third of the state’s water. This year, for the first time in 75 years of measuring, officials said that they found “no snow whatsoever.”

“The idea of your nice little green grass getting lots of water every day, that’s going to be a thing of the past,” Brown (D) said. California has been hardest hit by the drought, which has shattered records across the West, with Oregon and Washington also reporting their lowest snowpacks this year.

The governor’s order affects everyone from Hollywood mansion owners with emerald lawns to golf-course operators and homeowners with backyard pools.

Brown said the state will provide financial incentives to help replace 50 million square feet of lawns with drought-tolerant landscaping that uses less water. The state wants to increase its use of recycled gray water for irrigation.

Rebates will be offered to consumers to replace old appliances with new models that are energy efficient. Watering ornamental grass on roadway medians is banned. Golf courses, cemeteries and other large landscapes must cut water use immediately. And new construction developments cannot use potable water without installing special water-efficient drip irrigation systems.

Crop farms and other agricultural operations will not be affected, state officials said, because many have been hard hit already. Last year, more than 400,000 acres were not planted as a result of drought, and 17,000 workers lost their jobs, said Karen Ross, secretary of the state’s Department of Food and Agriculture.

But farms must now take the added step of reporting “more water use . . . to state regulators, increasing the state’s ability to enforce against illegal diversions and waste and unreasonable use of water under today’s order,” according to the Brown administration.

Brown’s executive order is expected to go into effect in mid-May, after state officials develop regulations to give it teeth. Local water suppliers can expect fines of $10,000 per day for failing to meet the 25 percent reduction compared with 2013. The fines can be passed to individual violators, who could pay penalties of $500, according to Felicia Marcus, chairwoman of the State Water Resources Control Board.

In 2014, Brown called for a 20 percent voluntary water-use reduction by all Californians but failed to meet that goal. This year, he said, tougher measures were needed to reach a goal of 1.5 million acre-feet of water over the next nine months, an amount equal to the volume of water that is currently in Lake Oroville a few miles north of Sacramento.

A recent study by researchers at Stanford University said California is facing years with far more drought, as climate change drives up temperatures in the state well above average while precipitation remains normal. A NASA study said California is one of several states in the Southwest that will endure a 30-year megadrought starting around 2050 unless global greenhouse gas emissions are lowered.

The outlook for California is so dire that some water systems in the state have already instituted harsher restrictions than the governor called for. The Santa Clara Valley Water District, which includes San Jose, called for a 30 percent reduction several weeks ago.

Homeowners who water lawns more than twice a week risk a fine following an inspection triggered by a meter or a report by a neighbor, said Marty Grimes, a spokesman for the water district.

Household water use varies from city to city. For health reasons, each person is allowed at least 55 gallons per day. In California’s largest city, Los Angeles, each person uses about 90 gallons per day, according to state officials.

California’s drought is hurting more than humans. The state’s director of Fish and Wildlife, Chuck Bonham, said it counted the lowest-ever number of a fish called smelt last year and estimated a 95 percent mortality rate in salmon eggs and young fry, meaning that the winter spawning stock collapsed.

The executive director of the California Water Foundation called the low Sierra Nevada snow survey result alarming. “We are in store for what could be the most challenging summer our farms, our fish and our families have ever witnessed,” said Lester Snow. “Over the next several months, we will see rural communities run out of clean water, crops and trees left to wither, and streams and wetlands dried up, leaving fish and water fowl with nowhere to go.”

Madelyn J. Glickfeld, director of UCLA’s Water Resources Group, said the magnitude of the state’s drought “is sort of unexplored territory. This is a little worse than the drought we had in the late 1970s, but we have so many more people, so much more farmland.”

In the San Jose area, golf courses are pulling up grass in areas where no one plays, and allowing patches of fairways and greens to brown. But David Stivers, executive vice president of Pebble Beach Co., which operates a golf resort near coastal Monterey, said his predecessors saw this problem coming.

“We’re in a unique situation because we sponsored the building of a $67 million wastewater reclamation project that uses 100 percent recycled water for irrigation,” Stivers said.

Built in 1994, it uses sewer water as part of a partnership with the town of Pebble Beach and Carmel-by-the-Sea. “We’re looking for ways to conserve water every way we can,” Stivers said.

Reid Wilson contributed to this report.