What the South Branch Au Sable offers anglers

The South Branch Au Sable is a smaller, more technical trout stream than its main-stem cousin—clearer water, tighter casting lanes, and fish that demand precision. If you're coming from the lower Au Sable or from other Roscommon-area rivers, the South Branch feels like a step up in difficulty and a step down in size. The stream runs roughly 20 miles from its origin near Grayling down to its confluence with the main Au Sable near Mio, and it holds a solid population of brown trout and brook trout, with some rainbows mixed in.

The character of the South Branch changes as you move downstream. The upper reaches—accessible near Grayling—are narrow, spring-fed, and cold, with undercut banks and root systems that hold good fish in tight quarters. The middle section, where most anglers fish, widens slightly and develops more classic riffle-and-pool structure. The lower reaches flatten out and warm a bit, but they still fish well in spring and fall. Summer can be tough on all sections because the water gets warm and the fish move deep or into shade.

Key Takeaways

  • The South Branch is a small, clear stream that requires accurate casting and smaller flies than you'd use on the main Au Sable.
  • Brown trout dominate the middle and lower sections; brook trout are more common in the upper reaches and in tributary streams.
  • Spring (April through May) and fall (September through October) are the most reliable seasons; summer requires early morning or evening fishing in shade.
  • Public access points exist at several road crossings and through the Huron National Forest, but parking is limited and some stretches require permission.
  • Fly patterns that work include small nymphs (size 16–18), terrestrials in summer, and caddis patterns in late spring and early fall.

Where to fish and how to access the water

The South Branch has fewer developed access points than the main Au Sable, so you need to know where to look. The most popular section runs from the M-72 crossing near Grayling downstream to the Mio Dam area. M-72 itself has a small pullout on the north side of the road, though parking is tight. From there, you can wade upstream into the upper reaches or downstream into the middle section.

The Huron National Forest owns or manages much of the land along the South Branch, and you can fish on national forest property without a permit. Several forest service roads provide access: Forest Road 4124 near Grayling, and Forest Road 4127 near Mio both lead to parking areas within walking distance of the stream. These roads are not always well-marked, so a GPS or detailed map helps. The Michigan Department of Natural Resources website lists public access sites, though the descriptions are sometimes vague—calling ahead to the Grayling DNR office can save you a wasted trip.

Private land borders much of the South Branch, especially in the middle reaches. Do not cross fences or fish from private banks without permission. Some landowners allow fishing if you ask; others do not. Respect posted property, and you'll keep access open for everyone.

Seasonal patterns and water conditions

Spring is the most forgiving season on the South Branch. April and May bring cooler water, active fish, and longer feeding windows. Nymphs work best—small Pheasant Tails, Hare's Ears, and Copper Johns in sizes 16 and 18. The water is usually slightly off-color from snowmelt, which actually helps because the fish are less spooky. Streamers can also be effective in the deeper pools, especially early in the morning.

Summer (June through August) is the hardest time to fish the South Branch. The water warms quickly, and by mid-July many sections climb into the low 70s Fahrenheit—too warm for trout to feed actively during the day. Fish the first two hours after sunrise and the last two hours before sunset. Focus on the deepest pools and the shadiest banks. Terrestrial patterns—ants, beetles, grasshoppers—work better than nymphs because they're what the fish actually see falling into the water. Early morning caddis hatches can be excellent if you're on the water at first light.

Fall (September through October) rivals spring for fishing quality. Water temperatures drop back into the 50s, and the fish feed aggressively. Caddis hatches are reliable in late September and early October. Nymphs and small streamers work throughout the season. By late October, the water gets cold and clear, and the fishing can be exceptional for a few weeks before winter.

Winter fishing is possible but requires patience and a willingness to fish very slowly. The water is cold and clear, and the fish are lethargic. Small nymphs fished dead-drift in the deepest pools are your best bet. Many anglers skip winter on the South Branch and focus on the main Au Sable or other options.

Fly patterns and tackle that work

Downsize everything you'd use on the main Au Sable. The South Branch is a size 16 and 18 stream, not a size 12 stream. A 9-foot rod for 4-weight or 5-weight line is ideal—light enough to cast small flies accurately but strong enough to handle a 16-inch brown trout in current. A 9-foot leader tapered to 5X or 6X is standard. In summer, when the water is low and clear, go to 6X or even 7X.

Nymphs are the workhorse. Pheasant Tail, Hare's Ear, Copper John, and small Prince Nymphs in sizes 16 and 18 catch fish year-round. Tie a few with tungsten beads so they sink quickly in the deeper runs. Caddis pupae (Olive or Tan, size 16) are deadly in spring and fall. Dry flies matter less on the South Branch than on bigger, slower streams—the fish don't see as many insects drifting on the surface because the current is faster and the water is narrower. When you do see a hatch, small Elk Hair Caddis or Adams in size 16 or 18 work.

Streamers are underrated on the South Branch. A small Woolly Bugger (size 10 or 12, black or olive) or a Muddler Minnow fished tight to the banks can trigger strikes from bigger browns. Fish them early in the morning or in low-light conditions. Terrestrials—ants, beetles, grasshoppers—are essential in summer. Carry a few in sizes 14 and 16.

Fish species and what to expect

Brown trout are the dominant species on the South Branch, especially in the middle and lower reaches. They're typically 10 to 14 inches, with a few fish pushing 16 to 18 inches. The browns here are wild fish, not stocked, so they're selective and they spook easily. They hold in the deeper pools, under the banks, and in the current breaks behind rocks. A 14-inch brown on a 4-weight rod in a small stream is a genuine fight.

Brook trout are more common in the upper reaches and in the small tributaries that feed the South Branch. They're smaller than the browns—typically 8 to 11 inches—but they're also less cautious. If you want to catch more fish and have more fun, fish the upper section or the tributaries. If you want to catch bigger, tougher fish, focus on the middle and lower sections.

Rainbows are present but not abundant. You'll catch a few, especially in spring when the water is higher and colder. They tend to be in the faster current and in the deeper runs.

Regulations and what you need to know

Michigan's general trout regulations apply to the South Branch. You need a valid Michigan fishing license. The stream is open year-round, but there are seasonal restrictions: from April 1 through September 30, the daily limit is five trout of any species, with no more than three over 15 inches. From October 1 through March 31, the limit is three trout of any species, with no more than one over 15 inches. Artificial flies and lures only—no live bait.

Check the current Michigan fishing guide before you go, because regulations can change. The DNR website has the full text, and the Grayling office can answer specific questions. Some sections of the South Branch may have special restrictions (catch-and-release only, for example), so know the rules for the specific stretch you plan to fish.

When to visit and what to bring

Spring and fall are the best times. April, May, September, and October offer the most reliable fishing and the most comfortable weather. Summer is possible but requires early mornings and evening sessions. Winter is for dedicated anglers only.

Bring a net—the banks are often steep and slippery, and a net makes landing fish much easier. Polarized sunglasses are essential; the water is clear, and you'll spot fish before they spot you if you're wearing good glasses. Waders are necessary year-round; the water is cold even in summer. A small backpack with fly boxes, leader material, and a few tools is all you need. The South Branch is not a place for a full tackle bag.

Insect repellent matters in late spring and early summer. The mosquitoes and black flies can be brutal, especially in the slower sections and near the banks. A head net is not overkill.

Frequently Asked Questions

Can I fish the South Branch year-round?

Yes, the stream is open year-round under Michigan regulations. Spring and fall are the most productive seasons. Summer requires fishing early and late in the day. Winter is slow but possible if you're patient and willing to fish very small nymphs in the deepest pools.

Do I need a guide to fish the South Branch?

No, but the stream is technical and the access is scattered. If you're new to small trout streams or to the area, a guide can save you time and show you the best water. Several fly shops in Grayling offer guide services. If you go on your own, bring a detailed map and call the Grayling DNR office to confirm access before you drive out.

What's the difference between the South Branch and the main Au Sable?

The South Branch is smaller, clearer, and more technical. It requires smaller flies, more accurate casting, and more patience. The main Au Sable is bigger, warmer, and more forgiving—better for beginners or for anglers who want to cover more water and catch more fish. Both are worth fishing, and they're only 20 minutes apart.

Is the South Branch good for beginners?

Not really. The fish are selective, the casting lanes are tight, and the water is clear. If you're new to fly fishing, start on the main Au Sable or on one of the slower, wider sections of the Manistee. Once you have some experience, the South Branch is a great next step.

What fly shop should I visit in Grayling?

Grayling has several fly shops that stock local patterns and can give you current conditions and access advice. The shops also rent waders and sell licenses. Stop in before you fish—the staff know the South Branch better than any website can tell you.