have been cleared, meaning the pools have been deemed functional, empty and dry, or nonexistent or have been treated by pesticides or mosquito fish.

Of the 2,900 pools, 1,411 are inside the burn scar. Mosquito breeding typically occurs when night temperatures are close to 60 degrees for five or more days at a time.

This week the district, an agency with 33 full-time employees, had two crews of three people working in Altadena on pool treatments. An additional crew placed mosquito fish in pools, which is a longer-lasting solution than chemical treatments but is possible only if the water quality is good enough for the fish to survive. For many of the pools, the district will have to return in the coming weeks to reassess the water quality before being able to use mosquito fish.

To help keep up with the demand, the district received support from the Greater Los Angeles County Vector Control District, which provided three technicians.

One of those technicians, Vector Control Specialist David Lopez, sat in the bed of a San Gabriel Valley district truck as it made its way around Altadena on a recent Tuesday afternoon.

Covered head to toe in personal protective gear, Lopez traversed the destroyed remains of homes on Beverly Way, near Mendocino Street, and threw a larvicide treatment into two pools surrounded by nothing but rubble. The larvicide is effective for 90 days.

The treatment targets mosquito larvae and is held in a net with pool-noodle like material inside to help it float on the surface of the water. A mosquito can go from larva to flying adult in five to seven days in the right conditions.

Diaz said the San Gabriel Valley district expects to complete the first round of treatments inside the burn area within the next four weeks.

“Our district has a scheduled aerial surveillance update at the end of the month/early May at which point technicians will take another look at flagged properties,” Diaz said. “We can determine if the number of pools we need to treat has decreased or increased.”

Technicians have observed mosquitoes breeding in most of the pools they’ve treated so far. However, technicians are not looking for signs of mosquitoes to determine whether to treat impacted pools.

“We can assume that if there is stagnant water in the pool, there is active breeding of mosquitoes. They are prioritizing getting to as many pools as possible rather than verifying if the pool is breeding at each visit,” Diaz said. “Whether it’s this week or next week, the pool will breed mosquitoes as long as it has stagnant water.”