How to Get Rid of Mosquito Larvae in a Pool

Why do I have mosquito larvae in my pool?

You have mosquito larvae because the water went still and the chlorine ran out. Mosquitoes lay their eggs on calm, standing water, and the eggs hatch into larvae that live in the top inch of the pool, breathing air through a little siphon at the surface. A pool with the pump off and no sanitizer is exactly the quiet, untreated water they look for, which is why wigglers almost always mean the pool has been neglected, left to go green, or closed under a cover that is holding rainwater.

A clean, running pool does not give them the chance. Moving water and a working filter make a pool a poor breeding site, because the surface agitation from the return jets stops females from laying and keeps larvae from hanging at the top to breathe. Add a free chlorine level in the normal 1 to 3 ppm range and the water is sanitized on top of being in motion. Mosquitoes will pick the bucket by your back door or the saucer under a plant long before they pick a pool that circulates.

The usual culprit is a pool that slipped. A pump that has been off for days, water that has turned green, or algae along the walls all tell you the chlorine has lapsed, and green water in particular gives the larvae food and cover at the same time. The other common source is a pool cover with a puddle of rainwater sitting on top, which is a small, warm, untreated pond that can breed thousands of mosquitoes while the pool underneath looks fine.

How do you get rid of mosquito larvae in a pool fast?

Clear them fast by running the pump around the clock, restoring the chlorine, and skimming the larvae off the surface. Start the pump and leave it running. Circulation is the single quickest change, because it breaks up the still surface the wigglers need to breathe and pulls them into the skimmer and filter. A pool that has been sitting with the pump off will often show far fewer larvae within a day of steady circulation alone.

At the same time, get the free chlorine back up by shocking the pool. Mosquito larvae are not especially tough, but low or zero chlorine is what let them survive in the first place, so bring the level up rather than relying on the trickle that was already failing. Use the pool shock calculator for the amount. If the water is green, treat it as an algae cleanup first, because the algae is both their food and their cover and the pool will not clear until it is gone.

Then skim the surface hard with a fine-mesh net. Wigglers cluster in the top inch of the water, so a fine skimmer net dragged slowly across the surface lifts out huge numbers in a few passes, especially along the edges and in the calm corners. Empty the skimmer and pump baskets afterward, since the pump will have drawn a lot of them in. Skimming plus circulation plus chlorine, run together, clears a larvae outbreak in a day or two.

What kills mosquito larvae in pool water?

In the pool itself, chlorine and your filter do the killing, backed by circulation. Larvae cannot survive sanitized, moving water for long, so a shocked pool with the pump running strains them out and finishes them off without any special product. There is no need to buy a dedicated mosquito chemical for a pool that has working equipment; the same chlorine and filtration that keep the water safe to swim in are what end the larvae.

For standing water that is not the pool, the targeted tool is Bti, sold as mosquito dunks or bits. Bti is a natural bacterium (Bacillus thuringiensis israelensis) that kills only mosquito, blackfly, and fungus-gnat larvae and is harmless to people, pets, birds, and fish. It is made for rain barrels, ponds, clogged gutters, and the puddle of water sitting on a pool cover, not for treating a functioning pool. If your cover is the breeding site, a dunk floating in that water is the clean fix while you keep the pool below it chlorinated.

You will see dish soap recommended, and it does work in the right place. A few drops of Dawn in a bucket of standing water breaks the surface tension so larvae cannot hang at the top to breathe, and they drown. That is a fine trick for a bucket, a birdbath, or trapped water you are about to dump, but do not pour dish soap into your pool. It foams the water, fouls the filter, and does nothing you cannot do better with the chlorine and pump you already have.

Can mosquitoes breed in a chlorinated pool?

Not in a pool that is actually being chlorinated and circulated. A pool holding a steady 1 to 3 ppm of free chlorine with the pump running on a daily schedule is not a viable nursery, because the water is sanitized, the surface is moving, and the filter is pulling in anything that tries to settle at the top. Finding wigglers is itself the evidence that one of those things has failed, almost always the chlorine, the circulation, or both.

It helps to understand that the moving, filtered surface matters as much as the chlorine does. A low chlorine reading on its own will not instantly kill every larva, but mosquitoes struggle to even lay eggs on water that is being pushed around by return jets, and larvae that cannot rest at a calm surface cannot breathe. That combination is why a well-kept pool stays mosquito-free even in peak season while the quiet puddle next to it swarms.

The flip side is a real public-health problem. A neglected or abandoned green pool is one of the most productive mosquito breeders a neighborhood can have, capable of hatching enough mosquitoes to affect homes for blocks around, which is why many counties will treat or stock an abandoned pool with mosquitofish if they find one. The lesson for your own pool is simple: the attraction is stagnation, not the pool, so keep the water moving and treated and it will never be the source.

Is it safe to swim in a pool with mosquito larvae?

No. Larvae mean the pool is unsanitized, so it is not safe to swim until you fix the water. Wigglers only survive because the free chlorine has dropped too low to do its job, and chlorine that cannot kill mosquito larvae also is not protecting you from the bacteria and other microbes that go with untreated water. Treat a larvae outbreak the same way you would treat a green pool: clear it and get the chlorine back in range before anyone gets in.

The larvae themselves do not bite or burrow, so the danger is not the wigglers in the water with you. The real issue is what they become and what they signal. Left alone, the larvae turn into biting adult mosquitoes in about a week to ten days, and adult mosquitoes are the ones that spread West Nile virus, Zika, and other diseases. Clearing the pool fast is as much about cutting off that next generation as it is about the water you are standing in.

Once the pump has run, the pool is shocked, and the larvae are skimmed out, test the water and wait until free chlorine is back down to 1 to 3 ppm before swimming. The ideal chemistry levels page covers the full set of readings to confirm, and the point is to swim in water that reads clean, not water that merely looks clear again. If you had to shock heavily, give it the usual time to come back down first.

How do you keep mosquito larvae from coming back?

Keep larvae away by keeping the pool chlorinated and circulating, and by never letting water sit still anywhere nearby. Hold free chlorine at 1 to 3 ppm and run the pump every day, longer in the heat of summer when mosquitoes breed fastest. A pool on a steady maintenance schedule simply never offers them the quiet, untreated water they need, so the whole problem disappears on its own.

Pay special attention to the cover. A pool cover that collects rainwater is the most common hidden mosquito breeder of all, since the pool below looks fine while a shallow pond grows on top. Pump the water off the cover with a cover pump after every rain, or drop a Bti dunk in any water you cannot fully clear, so the cover never becomes the nursery the pool is not.

Then clear the rest of the yard, because the mosquitoes that find the pool flew in from somewhere. Empty anything that holds standing water: buckets, kids' toys, plant saucers, old tires, wheelbarrows, and clogged gutters, and change birdbath water weekly. Keeping the pool clean also starves the other insects and frogs that a neglected pool attracts, so one habit, not letting water go stagnant, solves several pest problems at once.

Frequently asked questions