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Climate and Environment

Rainwater In Your Empty Pool? Here’s What To Do Before The Mosquitoes Take Over

A girl, partially obscured, swims in the bright blue water of a swimming pool.
This pool is full, but empty pools with standing rainwater are an ideal breeding ground for mosquitoes.
(Rachel Carr
LAist Featured Photos pool on Flickr)
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The recent storms have abated and given way to sunshine, but with that comes a bit of not-great news: a jump in the mosquito population.

Los Angeles County vector control officials say that on one hand, the heavy rains have helped flush out the underground storm drain system, one place where mosquitoes breed.

But then there are L.A.’s back yards.

“It does create a big issue for us in terms of our swimming pools and other backyard containers,” said Steve Vetrone, director of scientific-technical services for the Greater L.A. County Vector Control District. “We have about 5,000 unmaintained swimming pools in our database. And many of those are dry during the season, but unfortunately when it does rain like this, it does fill those up, and those are going to start producing mosquitoes for us.”

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Mosquitoes can spread diseases like West Nile Virus, which has sickened more than 7,000 people and killed more than 300 in California since 2003, according to the state public health department.

Unmaintained pools can be pools that are not in operation and are regularly dry, or filled “green pools” that are neglected and can produce mosquitoes.

“If the pool is full and crystal-clear blue and in operation, then these are not going to be creating any mosquitoes for us,” Vetrone said.

Worst of all is that as the air temperature rises, so does the temperature of standing water — and voila, new mosquitoes are spawned very quickly: “From egg to adult in about a week or so,” he said.

Pump it … or call for help

Homeowners who find themselves with standing water in a previously empty pool are advised to pump it out, Vetrone said. If your pool has no mechanism for doing so, you can rent a pump to get the water out. Another alternative is to call your local vector control district.

“We can come out and do the necessary treatment with chemicals that we know will do a very good job at controlling those immature mosquito stages,” he said.

What if the problem pool is elsewhere? It’s OK to call, Vetrone said.

“If a resident calls about a neighbor’s swimming pool, there's always anonymity that we try to protect there,” he said. “We're not looking to get anyone in trouble. We just want to make sure there aren't any mosquitoes that are coming off of those particular swimming pools that are unmaintained.”

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Vector control will be in touch

While some vector control districts still do flyover inspections, the Greater L.A. County district has in recent years used satellite images to keep tabs on unmaintained pools, Vetrone said, allowing it to flag problem pools and notify their owners.

So people with empty or unmaintained pools can also expect to hear from vector control officials in the near future with instructions on how to send in photos of their pools.

“And if that pool is in operation, then they'll be removed from the list,” Vetrone said. Or “depending on what the state of that swimming pool is, then we can make arrangements to visit that particular property.”

By the way, Vetrone added, pools are not the only culprit. Hot tubs, fountains, ponds, bird baths, even the saucers under flower pots can become spots for mosquitoes to breed.

“Take a walk around the house, make sure that you're not creating any breeding sources for mosquitoes,” he said. “And … dump and drain any standing water.”

More tips

The Greater Los Angeles Vector Control District has more information about unmaintained pools here, and offers these general mosquito control tips:

  • Eliminate standing water in clogged rain gutters, rain barrels, discarded tires, buckets, watering troughs or anything that holds water for more than a week.
  • Ensure that swimming pools, spas, and ponds are properly maintained.
  • Change the water in pet dishes, birdbaths, and other small containers weekly.
  • Request mosquitofish from your local vector control district for placement in ornamental ponds.
  • Wear EPA-recommended insect repellent when outdoors where mosquitoes may be present.
  • Report neglected (green) swimming pools in your neighborhood to your vector control district.

The district’s website has more information. A list of other vector control districts in Southern California can be found here.

What questions do you have about Southern California?

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