Unused Swimming Pools and Mosquito Breeding

A swimming pool that is not in use, because of a closure, a break between seasons or neglect, quickly turns green and still. Within days, it can become a prolific breeding site for mosquitoes, and a single pool can affect a whole neighbourhood.

This guide explains how to prevent it, and what to do if it has already happened.

The short answer

Unused pools breed mosquitoes when the water stops circulating, chlorine or sanitiser levels fall, and leaves and debris collect. To prevent this, keep the pool circulating and sanitised even when not in use, or fully drain and dry it, and cover it with a tight cover that stops water collecting on top. Remove debris, keep surrounding areas free of puddles, check regularly for larvae, and treat with suitable larvicide or restore sanitation if breeding occurs. Societies and owners should include pools in routine mosquito control, and report neglected pools to the right authority.

Why unused pools are a problem

• Still water allows mosquitoes to lay eggs.
• Algae and organic matter feed larvae.
• Sanitiser levels drop, so larvae survive.
• Covers that sag collect rainwater, creating breeding sites on top.
• Pump rooms, balance tanks and overflow channels can hold water too.

Prevention

1. Keep it running: If the pool is kept full, keep the pump and filter running regularly and maintain sanitiser levels.
2. Or empty it: If it will not be used for long, drain it completely according to the manufacturer's and a professional's advice, since empty pools can be damaged by groundwater pressure, and keep it dry and clean.
3. Cover it: Use a well-fitted cover that does not sag. Pump off any water that collects on it.
4. Remove debris: Skim leaves and clear drains and skimmers.
5. Check regularly: Look for larvae in the pool, cover, balance tank, overflow channels and surrounding puddles.

If breeding has started

• Restore circulation and sanitation as soon as practical.
• Scoop larvae and pupae where possible.
• For pools not about to be used, a professional can apply an appropriate larvicide.
• Do not allow bathing in the water until it has been properly sanitised and cleared.

Surroundings

• Keep drains, pool decks and surrounding areas free of puddles.
• Empty containers, buckets and loungers that collect water.
• Trim dense vegetation close to the pool.

For societies and clubs

• Include pools in the weekly mosquito control checklist, even when closed.
• Assign responsibility for maintenance during closures.
• Keep logs of inspections and treatments.

Neglected pools next door

If a neighbouring pool is breeding mosquitoes, speak to the owner or society politely, and, if necessary, report it to the local authority with photos and dates.

Safety

• Keep children and pets away from neglected pools.
• Do not mix pool chemicals. Follow instructions.

When to call a professional

A pool service and a pest control provider can restore the pool and treat breeding.

Frequently asked questions

Can mosquitoes breed in a chlorinated pool?

Not easily, if chlorine levels and circulation are maintained.

Is it safe to drain a pool?

Ask a professional, since draining can damage some pools.

Do pool covers help?

Yes, if they do not collect water on top.

How fast can larvae appear?

Within days of the water becoming still and unsanitised.

This guide is part of IPest's complete resource on mosquito control. For identification help, prevention and treatment options, see our full mosquito control guide for Bangalore.