Fish Flies Return to Windsor-Essex: A Natural Sign of Lake Erie’s Water Quality
- dstuebing
- Jun 17
- 3 min read
Essex Region – They’re back! Residents across Windsor, Essex County and Pelee Island are once again seeing mayflies, also known as fish flies, gather around shorelines, streetlights, windows and buildings. While their appearance can be messy and inconvenient, this annual emergence is an important natural event and a visible reminder that aquatic insects are part of a functioning Great Lakes ecosystem.
“Mayflies are an important part of the aquatic food web and have been around for thousands of years,” said Dr. Katie Stammler, Water Quality Scientist for the Essex Region Conservation Authority (ERCA). “Their presence tells us that parts of our lake and river systems are supporting the oxygen levels and habitat conditions these aquatic insects need. They also provide an important food source for fish and birds throughout the region.” She goes on to note that some mistakenly refer to these flying insects as June bugs, which are actually a type of ground beetle that emerges around the same time.
Mayflies spend most of their lives underwater as larvae, burrowed in lake and river sediments. They emerge as adults for 48 hours to mate, lay eggs and complete their life cycle. Because their larvae need oxygen-rich bottom sediments and are sensitive to poor water quality, a strong emergence is generally considered a positive sign for local waterways.
“Mayflies are often described as biological indicators because their presence reflects conditions in the water and sediments where they develop,” Dr. Stammler explains. “Healthy populations require suitable temperatures, adequate dissolved oxygen and sediments that are not severely degraded by pollution. When bottom waters lack oxygen or sediments are heavily contaminated, fish fly larvae can decline or disappear.”
But, fish flies do not mean that every water quality challenge has been solved. Lake Erie continues to face pressures from nutrient runoff, phosphorus loading, harmful algal blooms, shoreline development, changing weather patterns and other stressors. The annual hatch should be understood as one encouraging ecological signal among many indicators that scientists and watershed partners monitor to assess the health of the lake.
While fish flies are not unique to our region, the western basin of Lake Erie is especially well-known for large, highly visible hatches because local conditions can be favourable for mass emergence. When temperatures reach the range that triggers emergence, large numbers of larvae can leave the sediments around the same time. Wind direction, shoreline lighting and weather conditions can then concentrate adult fish flies in communities along the shore, making the event feel especially intense in our lakeside communities.
“The mayfly hatch is not exclusive to western Lake Erie, but the basin’s shallow water, productive habitat, extensive soft sediments and proximity to populated shorelines make the phenomenon more noticeable here than in many other places,” Stammler adds. While they may be in abundance now, the mayfly season typically only lasts a few weeks.
Actions that can be taken to reduce impacts include:
Reduce unnecessary outdoor lighting during peak emergence, especially near the shoreline, because fish flies are strongly attracted to light.
Use caution on sidewalks, roads, docks and stairs where dead fish flies may create slippery surfaces, particularly after rain.
Sweep or shovel accumulations into yard waste where permitted rather than washing them into storm drains.
Support local water quality by reducing fertilizer use, maintaining natural shoreline vegetation, keeping pollutants out of storm drains and supporting watershed restoration efforts.
“The best response is to recognize that mayflies are around for a short time each year and a long-term reminder of why water quality protection matters,” said Dr. Stammler. “Every action that reduces runoff and protects shoreline habitat helps strengthen the health of Lake Erie and the waters that define the Essex region.”
The Essex Region Conservation Authority is a public sector organization established by the Province of Ontario in 1973 and governed by local municipalities. For more than 50 years, it has delivered local programs and services that further the conservation, restoration, development and management of natural resources in watersheds in the Windsor-Essex-Pelee Island region.
