Fish flies back in Windsor-Essex, seen as sign of healthier waterways

Fish flies swarm Leamington, Ont., seen on June 25, 2025. (Chris Campbell/CTV News Windsor)

Fish flies, or mayflies, are back across Windsor-Essex, gathering around shorelines and lights.

Although messy and inconvenient, the Essex Region Conservation Authority (ERCA) says they’re actually a good sign for local water quality.

ERCA says mayflies live most of their lives underwater for two to five years and need oxygen-rich conditions, so strong hatches suggest parts of Lake Erie and local rivers are healthy.

However, officials stress their presence does not mean all water quality issues are solved, with ongoing concerns like nutrient runoff and algae blooms.

Speaking on AM800’s The Shift with Patty Handysides, Dr. Katie Stammler, water quality scientist for ERCA, says mayflies only live about 48 hours as adults, emerging briefly to mate and lay eggs.

“They mate under the lights, the males die and the females fly back to water to lay their eggs,” she said.

“At that point, the females and the males and everybody that’s died in the water become a really important source of food for our fish and our birds.”

Stammler says despite the nuisance, there’s no risk to people as they do not carry disease, and cannot bite.

“Fun fact about mayflies is that in that 48 hours that they live as adults they actually don’t feed at all,” she said.

“Both ends of their digestive tract are actually closed. So when you step on them and you hear that pop, it’s actually their digestive tract popping.”

Stammler says residents can reduce impacts by turning off outdoor lights to help limit the nuisance during peak season.

“It is a very short time that they’re around. It’s just for a couple of weeks that they’re at this sort of peak emergence and then they’ll be gone again,” she said.

“Just try to be patient with them.”

ERCA says fish flies should be disposed in yard waste where allowed, and avoid washing them into storm drains.