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- Approximately 2,700 swimming pools in and around the Eaton fire burn zone could become breeding grounds for mosquitoes as the weather warms up.
- Mosquitoes can spread diseases such as West Nile Virus and Dengue.
- A single swimming pool can be a breeding ground for as many as 3 million mosquitoes in one month.
As Los Angeles experiences its warmest temperatures of the season so far, officials in the San Gabriel Valley are warning residents that untended swimming pools and other standing water in the Eaton fire burn area could become breeding grounds for disease-carrying mosquitoes.
The destruction caused by January’s firestorm left behind “thousands of unmaintained swimming pools, damaged septic systems and debris-filled areas — ideal conditions for mosquitoes to grow,” said Jason Farned, district manager with the San Gabriel Valley Mosquito and Vector Control District, during a virtual community meeting last week. The district spans 26 cities in the Southland, including Altadena and Pasadena.
“Cooler weather has temporarily suppressed mosquito activity, but that will change quickly as we move further into spring,” Farned said. His warning was first reported by the Los Angeles Daily News.
Temperatures are forecast to remain warm but drop a few degrees Tuesday, before plummeting Wednesday as a cooling pattern spreads across the region.
Mosquitoes thrive in warm weather conditions and rely on standing water to breed, making the swimming pools fertile grounds for a population explosion. Temperatures in Altadena on Monday soared above 90 degrees, according to the National Weather Service.
Officials have identified approximately 2,700 swimming pools in the area that could be cause for concern, with about 1,300 pools inside the burn zone and about 1,400 on its perimeter, many of which are filled with ash and debris, said Anais Medina Diaz, a vector control district spokesperson.
The number does not account for septic tanks and ponds that may not have been spotted through aerial surveillance, Diaz said.
But a single swimming pool can breed as many as 3 million mosquitoes in one month.
“This is a huge concern for us,” Diaz said. “We’re really trying to focus on pools on the perimeter and work our way inward, because we want to make sure that the pools that are closest to communities that still have folks in them are not breeding or growing more mosquitoes and increasing the risk of disease transmission.”
Altadena families say they have been living at a fire-damaged apartment complex without gas or power. A legal consultant for the management company disputed those allegations.
One of the primary diseases of concern is West Nile Virus, an illness already endemic to most of the U.S., including the L.A. area, that can cause severe and potentially fatal brain inflammation, among other serious issues. There were 35 confirmed cases of West Nile Virus in L.A. County in 2024, including 27 hospitalizations and two deaths, according to data from the L.A. County Department of Public Health.
Dengue, another virus that can be spread by mosquitoes, can cause high fever, body aches, vomiting and a rash. L.A. County documented 234 cases of dengue infection last year.
Many of last year’s dengue cases were associated with travel to hot, humid places where the virus is commonly spread, such as the Caribbean. However, warming temperatures driven by climate change in Southern California also are contributing to a rise in local cases.
And although the flight range for the disease-carrying mosquitoes is typically limited to about a mile, anyone traveling into or around the Eaton fire burn area should be concerned about disease transmission, Diaz said.
The same is true for residents on the other side of L.A. County, where officials with the county’s West Vector Control District — which includes the Pacific Palisades area affected by the Palisades fire — said they are also bracing for mosquito issues this year.
“Swimming pools in the Palisades fire area are definitely a concern with regards to mosquito breeding,” Executive Director Aaron Arugay said in an email. “Our district will be responding throughout the summer to all requests for service regarding unmaintained pools in the Palisades fire area.”
The agency has not completed its estimate of the number of affected properties, Arugay said. But temperatures tend to rise earlier in inland areas than along the coast, which means mosquito activity in the Palisades likely won’t increase until later in the season.
Climate change is exacerbating the risk of potentially dangerous mosquito-borne diseases in California — threatening to turn more of those annoying-but-harmless bites into severe illnesses, experts say.
In Altadena, where the mercury is already beginning to climb, the coming weeks will be critical.
The agency’s treatment plan for affected pools includes the application of larvicides, which can provide up to 90 days of mosquito control.
Introducing mosquitofish (Gambusia affinis) — a species that eats mosquito larva and pupa — into the standing water sites is the most efficient way of limiting mosquito breeding; however, many of the fire-affected pools are not currently habitable by the fish due to ash and debris, Diaz said.
Farned said San Gabriel Valley Mosquito and Vector Control District officials will prioritize the work based on a property’s proximity to adjacent communities, as well as requests submitted by property owners.
“Standing water that fosters mosquito breeding is a violation of the public health and safety code, but we understand that many property owners currently have limited options for compliance, and so our goal is to provide as much support as possible during this transition period,” he said.
Officials in both fire-affected areas encouraged residents to reach out to their local agency to file service requests or notify them if they have swimming pools or spas that will not be maintained. Both agencies said there is no additional cost to property owners for requesting inspections or treatment.
However, costs could quickly balloon beyond what the San Gabriel Valley district maintains in its coffers, Diaz said. The agency collects a $20-per-parcel property tax each year, but will have to tap into its emergency reserves to cover the first round of mosquito treatment alone — an estimated $306,000.
The Eaton fire zone will need at least two more treatments this year, and may require an escalated response such as truck-mounted pesticide applications that cover a wider area, Diaz said. Additional funds could potentially come from resource requests fulfilled by the county or state, or reimbursements from the Federal Emergency Management Agency.
Although vector control districts have responded to wildfire burn areas in the past, Diaz noted that the scale of the Eaton fire’s destruction poses a challenge yet unseen in California.
“It’s unprecedented,” she said.
