Mosquitoes and the Drought

Great reminders from the Placer Mosquito and Vector Control District

Last Updated: 9/16/2015

With California’s current historical drought, there are many misconceptions floating around about how residents should store water and handle pools and fountains to contribute positively to the current state of emergency. The reality is many factors need to be taken into consideration, especially public health risks.

In drought conditions, mosquito sources are typically reduced in the spring and fall due to less rainfall. However, summer urban water use and irrigation occurs despite low rainfall and maintains many nuisance drainage-related mosquito sources. This means mosquito populations tend to thrive even during drought conditions.

Some drought measures can help address issues with mosquito and West Nile virus (WNV), while other strategies have the potential to increase mosquito and WNV exposure. It is critical that during these unprecedented warm and dry conditions, Californians do what is necessary to both support drought efforts and protect themselves from mosquito-transmitted diseases.

More and more Californians are collecting water in rain barrels as a tactic to address the drought. But without proper care, rain barrels can become a mosquito paradise in your backyard, increasing the risk of virus transmission in local communities.

Neglected swimming pools and containers that hold stagnant water can be prime spots for mosquitoes to lay their eggs, further increasing the risk of mosquito-borne diseases in local communities. Residents need to be especially mindful during this dry period to not let water conservation efforts bite back.


  • Any water that stands for a minimum of seven days around a home is designated as “standing water.” Common sources include: rain barrels, bird baths, trash cans, tires, pet bowls, flower pot saucers, boats, outdoor water features, hot tubs, wading pools, and non functioning swimming pools.
  • A neglected pool has abundant organic matter or bacterial growth, often with leaves or other debris, resulting in green to blackish-colored water. These pools are not properly maintained with filtration and chemicals and are generally neglected by the property-owner.
  • Covered pools can also attract mosquitoes. Water on top of pool covers will breed mosquitoes and if the pool isn’t completely sealed by the cover, water underneath will also breed mosquitoes.
  • Dump and drain standing water sources to prevent collection of water. Change water in pet bowls, bird baths, and wading pools at least weekly.
  • Seal openings of rain barrels with a screen (mesh size recommended 1/16” or smaller), maintain screens, look for immature mosquitoes in the water and if present treat frequently with an EPA-approved mosquito control product, and dry out and flip over barrels for long-term storage, so water doesn’t stand in the bottom.
  • Ensure your swimming pool’s filtration system is working properly and apply chemical treatments to prevent mosquito breeding, or drain a neglected pool completely and ensure it cannot hold water in the future.
  • Contact the District about non functioning pools and other areas of standing water around your area.