Residents of an East Sussex town say they are being "bombarded" by flies from a nearby sewage treatment plant.
More than 600 people have signed a petition calling for action to control repeated insect outbreaks in Uckfield.
Southern Water said treatment works across the country were experiencing problems with large numbers of flies.
Pesticides had proven ineffective and it was trialling the use of nets, while considering introducing natural predators like bats, it said.
Mark Lucas said he could often not use his garden due to insect "swarms".
"You cannot have a window open, you cannot be outside when they're bad," he said.
He has regularly had to throw food away because a fly had landed in his meal.
"God knows what bacteria they are bringing with them", he said.
When he first moved in several years ago Mr Lucas would witness "swarms" for a few days each year, but he said he now sees them "every single week."
A petition said residents were "unable to enjoy our gardens without being bombarded" by "huge swarms of little flies".
"They swarm around your head, they are really persistent," resident Den Banfield said, adding: "They get in your hair, they get in your mouth."
Professor Richard Hopkins, an entomologist at the Natural Resources Institute at the University of Greenwich, said flies from wastewater treatment works were "generally regarded as nuisance, rather than a direct human health risk".
However, he said German researchers published a study last year that "indicated that they can carry harmful bacteria with them into sterile environments".
He said the use of pesticides to control insects at treatment works was complicated, because "many of the chemical pesticides are particularly inappropriate for putting into water systems due to the sensitivity of those ecosystems to harm from these compounds".
Southern Water said it recognised that an increase in flies had been "distressing for residents," adding that it was reviewing its control measures "to ensure that we control these populations of non-biting midges from our site".
It said it was only permitted to use one "chemical agent" - known as bacillus thuringiensis israelensis - which had "not always managed to control the issue".
The problem is worse after periods of heavy rain, as the chemical agent is washed out and diluted, it said.