(AP) — California will kill 3.2 million trout to stop the outbreak of a bacterial infection that’s threatening hatcheries, wildlife officials said Monday.

The trout, which are used to stock waterways for recreational fishing, are in two hatcheries in the Owens Valley in the eastern Sierra and one hatchery in the Mojave Desert city of Victorville, northeast of Los Angeles.

Fish at the hatcheries have been infected with Lactococcus garvieae, which is similar to streptococcus, wildlife officials said.

“We didn’t have any other choice at this point. Our treatments weren’t working,” said Jay Rowan, environmental program manager for the wildlife department’s hatcheries.

Killing the fish and disinfecting the facilities was “the best option we have available” to restore use of the hatcheries in the shortest amount of time, Rowan said.

Outbreaks have been reported in fresh and saltwater fish farms and shellfish hatcheries but also cattle and poultry farms around the world, according to a statement from the California Department of Fish and Wildlife.

However, the bacterium had never been detected in fish in California before it was found at the Victorville facility in April. About 60,000 fish have since died.

The fish to be killed are at Mojave River Hatchery, Black Rock Hatchery and Fish Springs Hatchery. All three facilities had been under quarantine for more than a month. Testing hasn’t found any bacteria at Hot Creek Hatchery in the eastern Sierra, authorities said.

The depopulation could begin as early as next week and could last up to four weeks, Rowan said.

“It’s going to be a huge effort,” he said.

Infected fish can “show symptoms including bulging eyes, lethargic or erratic swimming and increased mortality, or be asymptomatic and show no signs of infection,” the wildlife agency said in a statement.

Transmitting the bacteria from fish or animals to humans is “rare and unlikely” but there have been a few cases of people with weakened immune systems getting it from infected raw fish and unpasteurized milk products, the statement said.

Rowan said it’s unclear how the fish were infected but the strain of the bacterium matches that found in the Columbia River in Washington state. One possibility is that migrating birds visiting the California hatcheries brought the bacterium in their feces but investigators are still working on the cause, Rowan said.

“We may never find out exactly how this got in,” he said.

Other California hatcheries still have tens of millions of trout but the fish kills will “have a significant impact for a long period of time,” he added.

The agency is looking at possibly moving some fish from central and northern hatcheries to stock some waters in the eastern Sierra and Southern California.