The Au Sable is the river that shaped Midwestern fly fishing, and the best of it is still being fished. The Hex hatch — massive golden mayflies emerging after dark in late June and early July while the largest brown trout in the river feed at the surface until midnight — is the reason most anglers plan their trips around the calendar rather than the other way around.
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The formal season opens on the last Saturday of April, when midges are active and the Hendrickson hatch begins on warm afternoons. May through early July is the richest stretch of the season: Hendricksons give way to caddis, which give way to Brown Drakes, which build toward the Hex. The Hex itself — late June to mid-July — is the single most time-sensitive hatch event in the Midwest, requiring advance booking of months and guide arrangements made even earlier. Summer settles into caddis-dominated evenings and August Trico spinner falls at dawn. Fall brings the Blue-Winged Olive back for a second act coinciding with pre-spawn brown trout that move into the shallows and become aggressive. October and early November produce some of the season's largest fish on streamers before the season closes.
The Au Sable runs cold and clear through the northern Lower Peninsula of Michigan, fed by spring seeps that keep temperatures honest well into summer — a significant advantage in a state that can deliver summer heat. The Holy Water, the catch-and-release artificial-lures-only section near Grayling, is the most famous and most pressured trout water in the state: fish density exceptional, hatch diversity outstanding across the season, and the tradition of fishing here running through multiple generations of Michigan anglers. The Au Sable riverboat — low, flat-bottomed, poled silently downstream by a guide standing at the stern with a long push pole — was developed specifically for this water and remains its signature experience. Night fishing from a riverboat during the Hex is the quintessential Au Sable trip. The river's branches and main stem sections away from the primary access points offer more solitude for those willing to explore the system beyond the Holy Water.
Grayling is the base camp: a small northern Michigan town with guide services, fly shops, and enough local infrastructure to support a fishing crew without distraction. The Holy Water puts the best fishing close, but the broader Au Sable system is worth exploring for anglers who want to get off the most-pressured water. Book guides for the Hex period six months in advance at minimum — the best are consistently spoken for well before the season opens.
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