Swarms of midges have been upsetting residents living close to the Christchurch City Council's wastewater treatment plant.

Swarms of midges have plagued residents in a Christchurch street this summer, forcing them to keep their windows and doors shut.

An infestation of the tiny insects has prevented residents in Aranui's Shortland St from having barbecues outside or even doing the gardening.

Resident Janet Profit said she sometimes wore a mask and raincoat when walking her dogs to protect herself.

"They just swarm on you. They get in your clothes and in your mouth."

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The midges were worse at night, but were still there during the day, she said.

"You don't turn a light on at night time. I keep everything shut and cannot have a barbecue or do gardening outside. They are everywhere."

The non-biting New Zealand native species attracted hundreds of birds, who feasted on the midges and left their droppings behind.

"The swallows stay here to have breakfast and they make a mess everywhere. You have no idea what my concrete looks like."

Another resident, who did not want to be named, said the midges were "just diabolical."

"You can't walk out the door without getting them in your ears and your mouth."

The midges first became a problem in 2007 and have progressively got worse since then, the residents said.

Last year, for the first time, the midges stayed around in winter too, Profit said.

The midge population had reduced in the past 10 days, but Profit was not sure if it was due to the colder weather or measures undertaken by the Christchurch City Council to control the insects.

The insects breed at the nearby wastewater treatment plant. Residents have complained to the council and signed petitions over the years to get action.

Council wastewater treatment manager Gijs Hoven said the combination of hot days and long periods of cool weather caused a concentrated spike in midge numbers this year.

The council has approached a number of pest control companies throughout New Zealand and was using an insect hormone called S-Methoprene to limit midge numbers.

"Any chemicals used for midges control must comply with the treatment plant's resource consents and not affect bird life."

The council was unable to do a bulk application of airborne insecticides over the entire ponds, but was experimenting with point spraying, Hoven said.

It was clearing vegetation around the oxidation ponds to reduce breeding habitats. It had started a project to monitor midge populations and help test future midge control measures.

Midges breed in freshwater and improved treatment at the plant meant cleaner water was entering the oxidation ponds. This had contributed to a midge population increase in the past 10 years, Hoven said.