The San Gabriel Valley Mosquito and Vector Control District this week sounded the alarm on a potential public health emergency sitting in the thousands of unmaintained swimming pools in and around the Eaton fire burn area.
At an online community meeting, District Manager Jason Farned said the district, which serves 26 cities and portions of unincorporated county including Altadena, has enhanced mosquito surveillance, monitoring mosquito populations and preparing to test samples for diseases.
“The destruction has left behind thousands of unmaintained swimming pools, damaged septic systems in debris filled areas,” Farned said. “Ideal conditions for mosquitos to grow.”
Since early February, the district has been working to identify how many pools are within the burn area or in neighboring communities that have been impacted by the fire.
Through the use of aerial footage, the district said there are nearly 5,000 pools in and around the burn area. About 1,300 pools are in the burn area, but those numbers may not include above-ground swimming pools, ponds or septic tanks.
In a typical year, the control district regularly monitors and services about 3,200 pools district-wide year-round.
Communications Director Anais Medina Diaz said environmental conditions are currently on the district’s side, but that will soon change.
As early as next week highs will hit the 80s. Mosquito breeding typically ramps up when overnight temperatures are closer to 60 degrees for five or more days at a time, which usually comes in mid-April or early May.
It takes a mosquito five to seven days to go from egg to flying adult in stagnant water. Diseases activity in mosquito populations begin around the end of May or early June as temperatures continue to climb.
West Nile virus and dengue are two diseases that can be spread by a mosquito bite.
In 2024, there were almost a dozen locally acquired cases of dengue in Los Angeles County. In addition, positive cases of West Nile virus were found last year in mosquitoes tested in San Gabriel Valley cities including El Monte, Baldwin Park, Azusa, Bradbury and Irwindale.
Diaz said one unmaintained full swimming pool can breed up to 3 million mosquitoes in one month.
“Beginning our efforts now will help us get in a good position to control mosquitoes before all of those environmental factors are working against us,” Diaz said.
Treatments include chemicals like larvicides which typically lasts for about 90 days before needing to be treated again or biological treatments like mosquito fish which is a longer lasting solution. However, Diaz said early assessments of the pools in the burn area show that the water quality is not suitable for mosquito fish to be able to survive.
On March 17, teams began heading out into the field to assess the conditions and test out personal protective equipment. Diaz said the goal is to complete the initial phase of treatments on pools within the next four to six weeks.
Priority will go to pools closer to populated communities and property owners who request a response from the district. The district has about 35 full-time staff members and brings on seasonal employees during the year but in normal circumstances it relies on residents to maintain pools and report potential issues.
Impacted residents are encouraged to submit a request for the district to respond to their pool and sign up for the SGVpools program, a communication channel used to inform residents of actions taken in the area.
Swimming pools on properties that burned down were filled with debris. Much of surrounding pool decks and outdoor decorations survived the flames from being close to a body of water. The pools themselves, now two months after the fire, appeared dark, with some having a green algae look to them.
Several pools in the area around Farnsworth Park appeared to be completely full.
“This is such an unprecedented time for residents and so they’re worrying about a lot of things and we don’t want the pools to be one more thing,” Diaz said.
Vector control districts responded to similar issues in the aftermath of the Camp fire in Paradise, California. Diaz said six years later, treatment and management of pools impacted by the fire remains ongoing.
“It is a big undertaking,” Diaz said.