Different habitat
Lake Hexagenia nymphs burrow in sediment. Water-column oxygen and bottom habitat influence their populations. A fishable trout-river riffle doesn't behave like a Great Lakes bay.
Choose your lake
Buoy monitoring locations, not predicted swarm destinationsTODAY'S LAKE MAYFLY SIGNAL
Loading data…Saginaw Bay
Buoy water temperature
Checking…Measured surface, not sediment
Water trend
—Last two complete sampled days
Recent buoy wind
—Measured where available
Evening outlook
—NWS nearby shoreline weather
Collecting the last available NOAA buoy observation…
NOAA National Data Buoy Center · Open original buoy observations ·
Human-reviewed field evidence
Documented mass hatch events
A documented mass swarm is different from seeing one mayfly. Reports are held for manual source review and only published after a curator adds evidence to the approved event ledger. No report changes the water-temperature forecast automatically.
Reviewed events in selected regionChecking records…Only approved, source-linked events are published.
Recent documented events · 14 days—A past event never means insects are emerging now.
Checking editor-reviewed evidence…
Reports are submitted through a public GitHub Issue and require a GitHub account. Do not share exact coordinates, private addresses or personal details. Read the review standard.
Citizen-science evidence
Are people actually seeing Hexagenia?
Public, photo-backed, Research Grade Hexagenia identifications from iNaturalist in the selected region over the last year. These records help confirm that someone identified an insect; they do not verify a mass hatch or a specific emergence location.
Independent species IDs
Checking source…
Searching public regional records.
Mass emergence verification
Not verified by this tool
A Research Grade ID, even with a photo, does not document a swarm or lakebed hatch.
Recent documented specimens
Latest public recordsChecking observation records…
Reports are filtered by a regional search box that includes nearby land. Exact coordinates may be obscured; we intentionally do not pin specimens to shoreline locations. No observations is not evidence of no hatch. Taxonomic identifications can change.
Explore source observations on iNaturalist · Submit your own observation · iNaturalist API and responsible use
The 68°F emergence watch
Surface proxy, not lakebedMichigan Sea Grant describes a shallow western Lake Erie pattern: several days after lake-surface water reaches about 20°C (68°F), sediments may warm enough for Hexagenia to emerge. That timing is not proven for every Great Lakes site.
40°F60°F68°F watch80°F
Waiting for measured water history…
Buoy surface water68°F reference, not confirmed emergence
Sensor values, weather, and emergence are different observations. This tool cannot tell how many mayflies are present in the lake, whether the bottom has warmed, or where a windblown swarm will land.
Next seven evenings
6 PM–11 PM EasternCompare winds and rain forecast at nearby shoreline weather points during evening hours. Offshore winds can differ. Only the immediate weather watch uses today's fresh surface temperature; later dates have no water-temperature forecast.
Loading NOAA/NWS data…
A lake hatch isn't the Au Sable Hex hatch
Different 68°F meaning
Here, 68°F is a reported lake emergence-development reference. On the trout-river tool, 68°F is a caution for catch-and-release fishing. We do not mix the two rules.
Different confidence
A fresh NOAA buoy is evidence of water temperature, not evidence that Hexagenia are present. Historic Saginaw Bay and Lake Erie population studies don't establish current local abundance.
Scientific basis: Michigan Sea Grant: When will the mayflies arrive? · USGS: Burrowing mayflies in western Lake Erie and Saginaw Bay · USGS: Water quality and population dynamics.
Frequently asked questions
When do the Great Lakes mayflies hatch?
Hexagenia swarms commonly occur across June through August in shallow Great Lakes waters. In western Lake Erie the first big periods can begin in early summer, depending on bottom warming and nymph populations. There is no single statewide hatch date.
Does 68°F mean the mayflies are hatching tonight?
No. Michigan Sea Grant identifies about 20°C (68°F) at the sediment as a relevant biological threshold. A surface buoy reading is a proxy and may lead bottom temperature by days. We do not claim emergence has begun without observations.
Why does Saginaw Bay sometimes say temperature unavailable?
The Saginaw Bay buoy is seasonal and may not publish live water temperatures in autumn or winter. Missing and stale measurements are displayed honestly instead of substituting Toledo, a river gauge, or Lake Huron open-water averages.
Will the tracker tell me which shoreline gets the swarms?
Not yet. Wind direction and speed influence where airborne mayflies move, but a buoy and NWS point forecast cannot verify where insects emerged or where they will accumulate.
What's the difference between lake flies and Hex on the Au Sable?
Both can include large mayflies in the genus Hexagenia, but Great Lakes emergence depends on lake-bottom habitat and temperatures; the Au Sable tool focuses on trout-stream conditions and fly-fishing windows. Open the Au Sable mayfly predictor.