Following a decade of debates and political battles, the California Coastal Commission has approved a plan to build the largest ocean desalination plant ever built in Northern California.

The project, proposed at the site of a former sand mining plant on the Monterey Bay shoreline near the town of Marina in northern Monterey County, would be just one-tenth the size of the nation’s largest desalination plant, built in 2015 in Carlsbad, near San Diego.

But it would provide 4.8 million gallons a day of drinking water from the ocean — about 35% of the water supply for Monterey, Carmel, Pacific Grove and surrounding communities — many of which have suffered under water shortages for the past 25 years.

After a 12-hour public hearing in Salinas with more than 300 people testifying, the Coastal Commission voted 8-2 late Thursday night to approve the plan, which was supported by Gov. Gavin Newsom.

“We have a building moratorium. We have water rationing,” said Josh Stratton, a spokesman for California American Water, a private company that proposed the plant and which provides water to about 100,000 people in the Monterey Peninsula area. “There are multiple housing projects that haven’t gone forward. We already have some of the lowest per-capita water consumption in the state. This is critically needed.”

But opponents launched a passionate and sustained effort to kill it. They noted that under Cal-Am’s own projections, the project would increase water bills by 50% a month, adding about $50 to the average bill.

Critics included environmental groups and some local elected officials, particularly from the city of Marina, which has far more minority and low-income households than famously wealthy nearby communities like Pebble Beach and Carmel. They noted that Marina would get none of the water from the project since it isn’t served by Cal-Am Water.

“The water will be obscenely expensive,” said Melodie Chrislock, director of Public Water Now, a non-profit group that has been pushing for a public takeover of Cal-Am. “And it’s not fair to put it in Marina. They don’t get a drop of the water and they get all the environmental impacts.”

Cal-Am estimated the cost of the plant at about $330 million, but that estimate is several years old.

In the Coastal Commission’s staff report, the water’s cost was estimated at roughly $6,000 an acre foot. An acre foot, or 325,851 gallons, is enough water for two families of four for a year.

That cost is several times the price of water from other desalination plants, like the Carlsbad plant, which typically runs about $2,500 an acre foot, and more than three times the price of recycled water.

Critics say there’s a better approach: Continue to expand Pure Water Monterey, an advanced water recycling project run by the Monterey Peninsula Water Management District and Monterey One Water, the area’s wastewater operator, that recycles wastewater and puts it into underground aquifers.

“Building desal now is premature. It locks the Monterey Peninsula into an expensive solution,” said Mandy Sackett, California policy director for the Surfrider Foundation, an environmental group.

Supporters countered, however, that the water recycling project and groundwater wells in general were important, but not as “drought-proof” as the desalination project, given that underground water basins in the area have problems with sea water intrusion and also demands from farmers.

They also noted the desalination project would have little impact on wildlife. The plan is to drill up to seven slant wells 200 feet under the sea floor and slowly draw out ocean water through the sand. The wells would be based at the former CEMEX sand mining plant, which operated on the beach near Marina since 1906 and closed last year. Their pads and electrical equipment would take up 1 acre.

The seawater would be piped about two miles east to a desalination plant that would be constructed next to an existing wastewater treatment plant. The water would be piped to nearby cities. And the leftover brine would be blended with treated wastewater to get its salinity back to ocean water levels and released into the ocean through an existing pipe that empties two miles offshore into Monterey Bay.

California has been in a severe drought for 8 of the last 11 years. With climate change, Newsom has said that the state needs to expand its water supply by building more off-stream reservoirs, water recycling plants, stormwater capture projects and desalination plants.

The Monterey area has had a severe water shortage since 1995, when state regulators said Cal-Am was taking three times as much water from the Carmel River as it had rights to, and ordered cuts. Voters rejected plans for a new dam on the Carmel River, and several other desalination projects were proposed but never built.

There are 12 ocean desalination plants in California now. But most are small and serve military bases, power plants and other facilities, like the Monterey Bay Aquarium.