Hexagenia Limbata Peak Dates on the Au Sable River

The Short Answer

When Does the Hex Peak on the Au Sable?

The Hexagenia limbata hatch on the Au Sable River peaks during the last ten days of June in a typical year — historically June 20 through June 28. In 2026, with a cold spring running 3–4 weeks behind schedule, watch for the peak window to shift toward June 22 through July 2.

But "peak" is misleading. The Hex does not arrive like a train on a schedule. It responds to water temperature and atmospheric conditions. The hatch can be extraordinary one night, absent the next, and spectacular again the night after. Understanding what triggers it — and what shuts it down — is more useful than any specific calendar date.

The single most important number

Water temperature at 65°F (18°C) is the trigger. When the Au Sable holds above 65°F for several consecutive days, Hexagenia limbata nymphs begin their emergence. Track the USGS gauge at Mio for real-time water temperature before planning your trip.

Year-by-Year Timing

Historical Peak Windows — Au Sable Holy Water

The following windows are based on decades of guide reports, lodge records, and hatch data from the Grayling area. "Scout nights" are when the first isolated Hex appear. "Peak" is when the most fish are consistently rising to the hatch across the widest water.

Year	First Scout Nights	Peak Window	Season Character
2026Current	~Jun 8–12 (est.)	Jun 22 – Jul 2 (projected)	Cold spring — run delayed 10–14 days vs typical
Typical Year	Jun 5–10	Jun 20–28	Standard peak timing
Early Year	May 28 – Jun 3	Jun 10–20	Warm May, early trigger
Late Year	Jun 15–18	Jun 25 – Jul 5	Cold spring, delayed run

2026 Specific Conditions

Water temps on the Holy Water hit 65°F in the first week of June 2026 — approximately 10 days later than a typical year. Based on this data, the first reliable Hex nights should begin around June 10–14, with peak activity running June 22 through July 2. Monitor the USGS Grayling gauge daily starting June 10.

Night by Night

What a Hex Week Looks Like

Days 1–3: Scout Nights

First Isolated Emergences

Individual Hex nymphs begin emerging sporadically in the deepest, warmest pools — usually the flat water below Stephan Bridge Road. A few fish rise. The window is short, 45–60 minutes. Most anglers on the river this week will find nothing and conclude the hatch hasn't started. It has. Fish the slow outside bends at Keystone Landing.

Days 4–7: Building

Consistent Emergences Begin

The hatch becomes predictable. Fish are rising in multiple pools simultaneously. The window extends to 90 minutes. This is often the best fishing of the entire season — the fish are responding aggressively to the new food source and have not yet seen hundreds of size 4 Hex patterns. If you can only choose one week, this is it.

★

Days 8–14: Peak

Full Spinner Fall — Every Night

The hatch is in full eruption. Hex duns emerging from 9:30–11pm, spinner fall beginning after midnight and running until 2am. Multiple fish rising in every pool simultaneously. The river sounds like rain from the splashing. This is what anglers travel from across the country to witness. The window is 2.5 to 3 hours. Fish the spinner fall — it consistently produces the largest fish.

↓

Days 15–21: Declining

Waning but Still Worth Fishing

Emergence intensity drops but fish are still rising. The advantage: fish have now seen thousands of flies and are more selective — this is the week that separates anglers who understand the hatch from those who don't. Spinner patterns outperform duns in the waning weeks. Mouse patterns fished between rises produce consistently through the end of the Hex window.

Where to Fish

Best Au Sable Sections for the Hex Hatch

The Hex requires soft, silty bottom — the same slow flat water that defines the Holy Water from Burton's Landing to Wakeley Bridge. Not all sections of the Au Sable have equal Hex habitat.

Holy Water — Best Hex Sections

⭐ Burton's Landing to Stephan Bridge — classic Hex pools in the flat, slow inside bends

⭐ Stephan Bridge to Keystone — widest soft-bottom sections, highest nymph density

⭐ Keystone to Wakeley — deepest pools, largest fish, most consistent spinner fall

Below Wakeley — Also Excellent

✓ Wakeley to McMaster's — wider, slower, sandy-bottom Hex habitat; wade with caution (deep)

✓ McMaster's to Mio — Hex habitat intensifies; massive fish, limited access, boat preferred

✓ Below Mio Dam — trophy water but primarily drift boat water; guide recommended

What the guides won't always tell you

The biggest fish during the Hex hatch are not in the Holy Water — they're in the Stillwaters between Wakeley and McMaster's, and in the broad flat pools below Mio Dam. These are water where 24-inch browns are realistic targets. But wading is dangerous and drift boat access is essential. This is guide water.

What Kills the Hatch

Conditions That Pause or End the Hex

Understanding what shuts the Hex down is as important as knowing when it starts. The hatch is heavily weather-dependent.

❌ Hatch Killers

🌧 Rain during the emergence window — Hex nymphs stop emerging mid-hatch

💨 Wind above 10 mph — disrupts the spinner fall, dries blow off course

🌙 Full moon — bright moonlight suppresses emergence; new moon is ideal

🌡 Night temps below 60°F — nymphs retreat; can pause the hatch for 2–3 nights

📉 Barometric pressure drop — a falling barometer often shuts the hatch immediately

✅ Ideal Hex Conditions

🌡 Water temp 65–72°F, air temp above 68°F at 10pm

☁️ Overcast or hazy sky — reduces light penetration, extends the emergence window

🌙 New moon or cloudy night — darker conditions trigger heavier emergences

📈 Stable or rising barometric pressure — fish feed more aggressively

🌬 Calm or light variable wind — spinner fall lands on the water properly

How to Book

Getting a Guide Date Before They're Gone

Au Sable Hex guide dates book by February or March for the following June. If you are reading this in May or June, call immediately — last-minute cancellations do open but plan as if they will not.

Gates Au Sable Lodge (Stephan Bridge Road, Grayling) — the benchmark for Holy Water Hex fishing. Full-service lodge, guide trips, and fly shop. gateslodge.com

Old Au Sable Fly Shop (Grayling) — operating on the Au Sable since 1936. Excellent guide service and the most comprehensive local pattern selection. oldausable.com

Self-guided wading is very productive during the Hex and public access on the Holy Water is extensive. See our Au Sable Holy Water Access Guide for parking and wade-in points.

Ready for the Hex?

Live Au Sable conditions, water temperature, and this week's report — updated every Thursday.

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