AuSable River Trout Fishing Conditions

The stretch anglers call the Holy Water runs for roughly twelve miles between Grayling and Mio. Designated as flies-only, catch-and-release water by the Michigan DNR, this section has protected its wild brown trout population for decades. Fish here are educated, the current is honest, and the hatches are legendary. If you can fool a brown trout on the Holy Water, you can fish anywhere.

The AuSable is a freestone river fed by cold springs throughout its length, which keeps water temperatures in the trout-prime range well into summer when other rivers warm past the threshold. This makes the Holy Water a mid-July destination when most anglers have given up on surface fishing until fall. The springs also give the river its characteristic clarity: polarized glasses and patience let you see fish before you cast to them.

Reading the Conditions on the AuSable

The AuSable has eight USGS gauges, more than any other Michigan trout stream. The gauge at Grayling covers the Holy Water. When it reads between 200 and 400 cfs, the Holy Water is in its sweet spot: wadeable throughout, running clear, and the gravel runs are at the perfect depth for both wading anglers and feeding trout. At these flows, the classic dry fly water between Burton's Landing and Wakeley Bridge is at its best.

Above 500 cfs on the Grayling gauge, the Holy Water gets pushy. Wade carefully and avoid the deeper bends where the current undercuts the banks. The fish move to softer water: look for them in the slack behind logjams and in the shallow inside bends where the current spreads and slows. High water on the AuSable usually means the North Branch is also running strong, but the South Branch near Roscommon may still be fishable because its flatter gradient absorbs the extra water.

Below 150 cfs (typically mid to late summer), the AuSable gets low and clear. This is when the spring-fed nature of the river pays off: water temperatures stay in the mid-50s even when air temps hit 90°F. Low water on the Holy Water is technical fishing. The fish can see everything. Long leaders (12 feet minimum), 6X tippet, and downstream presentations become essential. But the payoff is that fish are concentrated in predictable pools and you can sight-fish to specific trout.

For the lower river below Mio Dam, the gauge at Mio tells a different story. This is bigger water with lake-run fish mixing in. Flows of 800 to 1,200 cfs at Mio are normal. The trophy brown trout section from Mio to McKinley Bridge fishes best in slightly elevated flows when the fish spread across the wider gravel flats. Streamers and heavy nymph rigs are the standard approach on this water.

Best Hatches on the AuSable

The AuSable hatch calendar is among the richest in the Midwest. Season opens in late April with Hendricksons emerging on warm afternoons: the Red Quill and Hendrickson Dry in sizes 12-14 fished in the afternoon between 2pm and 4pm will draw willing browns. May brings the Grannom caddis hatch in explosive numbers, and a well-skated Elk Hair Caddis on the surface can produce frantic takes.

Late June marks the arrival of the Hexagenia limbata: the Hex hatch. Massive, golden mayflies emerge after dark on warm, still evenings, drawing the largest brown trout in the river to the surface for several weeks. The AuSable Holy Water is ground zero for Hex fishing in Michigan. Anglers plan trips months in advance for this single event. Fishing an Extended Body Hex Dun on a moonless night to a slurping brown you can hear but not see is as thrilling as trout fishing gets.

Sulphurs follow the Hex into July, offering evening surface fishing through the peak of summer. White Fly emerges in August on the main stem. Fall brings the Blue-Winged Olive back for a second act, often coinciding with pre-spawn brown trout that are aggressive and highly visible in shallow riffles.

River Sections

The North Branch near Lovells holds exceptional wild brook trout in addition to browns. It is smaller and more technical than the main stem, requiring careful wading and shorter casts. The South Branch near Luzerne runs cold and clear through a different character of landscape: more remote and less pressured than the Holy Water. The main stem below Mio transitions toward a more migratory fishery with steelhead and walleye mixing in during their seasons.

Access and Regulations

The State of Michigan maintains numerous public access sites along the AuSable. Burton's Landing, Wakeley Bridge, Canoe Harbor, and Parmalee Bridge are among the most used on the Holy Water stretch. The DNR has made significant investments in public access infrastructure on this river over the past two decades, and most of the prime water is reachable without trespassing.

The Holy Water between Burton's Landing and Wakeley Bridge is flies-only, artificial lures only, catch-and-release year-round. The North Branch has its own special regulations. Check the current Michigan DNR Fishing Guide for exact boundaries before you fish. Regulations on the AuSable are enforced, and the conservation officers know the water.

When to Go

Season opens the last Saturday of April. The best fishing of the year is May through early July: Hendricksons, caddis, March Browns, and the build toward the Hex. Summer fishing remains surprisingly good given the spring-fed water temperatures. Fall in October brings aggressive pre-spawn browns and the second BWO hatch of the year. Some of the largest fish of the season are caught on streamers in October and early November before the season closes.