Poseidon Water sought to turn seawater into drinking water but activists said plan would devastate ecosystem on Pacific coast

A California coastal panel on Thursday rejected a longstanding proposal to build a $1.4bn seawater desalination plant to turn Pacific Ocean water into drinking water as the state grapples with persistent drought that is expected to worsen in coming years with climate change.

The state’s Coastal Commission voted unanimously to deny a permit for Poseidon Water to build a plant to produce 50m gallons of water a day in Huntington Beach, south-east of Los Angeles.

Poseidon said it was disappointed in the decision.

“California continues to face a punishing drought, with no end in sight,” a company statement said. “Every day, we see new calls for conservation as reservoir levels drop to dangerous lows. We firmly believe that this desalination project would have created a sustainable, drought-tolerant source of water.”

The vote came after a heated meeting before the commission attended by dozens of supporters and critics of the plan. It was considered a crucial decision on the future of the plant after years of other hearings and delays.

Poseidon’s long-running proposal was supported by Governor Gavin Newsom but faced ardent opposition from environmentalists who said drawing in large amounts of ocean water and releasing salty discharge back into the ocean would kill billions of tiny marine organisms that make up the base of the food chain along a large swath of the coast.

“The ocean is under attack” from climate change already, Commissioner Dayna Bochco said. “I cannot say in good conscience that this amount of damage is OK.”

Other critics said the water would be too expensive and was not urgently needed in the area where it would be built, which is less dependent on state and federal water due to an ample aquifer and water recycling program.

Commissioners cited those issues in following a staff recommendation and rejecting the proposal. They also cited the energy cost of running the plant and the fact that it would sit in an earthquake fault zone.

Before voting, the 12-member commission heard hours of comments from scores of people packed into a hotel meeting room in the Orange county city of Costa Mesa in addition to those tuning in online.

At the meeting, supporters wore orange and yellow construction vests and toted signs saying “support desal!”

Opponents carried signs reading “No Poseidon” and “Do not $ell our coast.” One woman who wore a plankton costume and held a sign reading “I am a plankton – please do not kill me!”

California has spent most of the last 15 years in drought conditions. Its normal wet season that runs from late fall to the end of winter was especially dry this year and as a result 95% of the state is classified as in severe drought.

Newsom last summer urged residents to cut consumption by 15%, but since then water usage has dropped by only about 3%. Some areas have begun instituting generally mild restrictions such as limiting how many days lawns can be watered. More stringent restrictions are likely later in the year.

Much of California’s water comes from melting snow and with a far below normal snowpack, state officials have told water agencies they will receive only 5% of what they have requested from state water supplies beyond what’s needed for critical activities like drinking and bathing.

Desalination removes salt and other elements from ocean water to make it drinkable. Those elements are discharged back into the sea, while the water can be channeled directly to consumers or used to replenish a groundwater basin. The country’s largest seawater desalination plant is already operating in nearby San Diego county, and there are also coastal plants in Florida.

The idea of desalination has been debated for decades in Huntington Beach, a coastal community south-east of Los Angeles known as “Surf City USA” that relies on its sands and waves for tourism. Discussion of the project has recently focused on the impact of climate change on regional water supplies and on sea level rise in the low-lying coastal area where the plant would be built.

More than two decades ago, Poseidon proposed building two desalination plants – the one in San Diego county, and one in Huntington Beach. The San Diego county plant was approved and built, and desalinated water now accounts for 10% of San Diego county water district’s water supplies.

But the Huntington Beach project has faced numerous delays. In 2013, the Coastal Commission voiced concerns that the proposed use of intake structures to quickly draw in large volumes of water from the ocean would damage marine life. Poseidon, which is owned by Brookfield Infrastructure Partners, conducted additional studies and resubmitted the plan with a proposal to mitigate marine damage through restoration of nearby wetlands.

• This story was corrected on 13 May. The California Coastal Commission meeting was on Thursday, not Wednesday.