LOS ANGELES — California officials were trying Monday to solve a stinky mystery: A die-off has left hundreds of fish floating in a recently restored lagoon on the tony Malibu coast.

Scientists believe the Malibu Lagoon die-off, which began last Wednesday, is likely caused by unusually warm water temperatures, said Craig Sap, superintendent of California State Parks’ Angeles District.

“We had many days in a row of warmer-than-usual temperatures. We hadn’t had much of a breeze down there to keep the temperatures down,” Sap said.

Other possibilities include elevated nutrient levels, dropping levels of dissolved oxygen or having too many fish in the lagoon. Officials are taking water samples and fish for testing.

Malibu Lagoon underwent a controversial restoration project in 2013.

Major conservation groups, including Sierra Club and Audubon Society chapters, backed the restoration, but others sued to stop the project, contending it would destroy sensitive wildlife habitat. The battle lasted for years but the project finally broke ground in 2012.

The die-off has raised locals’ concerns about what some call failures in the project.

Resident Wendy Dunn told KTLA that State Parks ignored plans for so-called breach points that would allow the lagoon water to mix with fresh ocean water to keep proper oxygen levels.

Sap said breaching manually would cause more damage to the ecosystem.

“What you end up doing is, some species that are not meant to be there get in, and species get flushed out when they shouldn’t have been,” Sap said.

He said the lagoon project improved the ecosystem by providing better oxygen levels and the number of fish in the lagoon has since increased.