SAN DIEGO -- Environmentalists announced a lawsuit Friday in an attempt to stop construction of a desalination plant in Carlsbad.

The lawsuit was filed Thursday in San Diego Superior Court by San Diego Coastkeeper and Surfrider Foundation, San Diego Chapter.

The suit claims that in violation of state law, the San Diego Regional Water Board did not analyze the plan to determine the best site, design and technology before conditionally approving construction of the Carlsbad Desalination Plant.

The groups claim they repeatedly raised concerns about the lack of analysis by the board.

A spokeswoman for the Regional Water Board, Judie Panneton, said officials wouldn't comment on the lawsuit until they were finished reviewing it.

In approving the plan, the water board acknowledged it was incomplete, lacking certainty and details, according to the lawsuit.

Nevertheless, the board chose to conditionally approve the plan, subject to submission of a new plan with amendments within six months of the conditional approval, according to the lawsuit.

According to Poseidon Resources Corp., which wants to build the $300 million plant, it would convert seawater into drinking water at a rate of about 50 million gallons a day -- about 9 percent of the county's current needs.

The plant would be located at Carlsbad's Agua Hedionda Lagoon, next to the existing Encina power plant, and would open in 2011.