The California drought has mosquito-control officers in the San Joaquin Valley worried that outbreaks of West Nile virus as well as dengue and yellow fevers may strike the populace again this year.

Fingers are being pointed at neglected swimming pools as perfect hatcheries for mosquitoes, which can carry the diseases and transmit them to humans. Last year, 29 Californians died of neurological complications from the West Nile virus and nearly 800 were infected.

Warm winter weather in 2015 has caused many mosquitoes to emerge early from hibernation. Concerned homeowners have subsequently been calling mosquito-control officers in greater numbers than usual. For example, the Fresno Mosquito & Vector Control District got 50 calls in February compared with the usual 12 to 16. “Certainly during drought years, we see an increase in West Nile virus,” Jodi Holeman of the Consolidated Mosquito Abatement District told the Fresno Bee.