107 CFS: Low Water and September’s Clarity Window
At 107 CFS this week, the Pueblo tailwater is running lean for early September. That’s below the low-summer threshold where gin-clear water starts to dominate and trout behavior shifts sharply. For perspective: this water’s winter profile runs stable and cold around 70–150 CFS and fishes predictably. Summer crisis territory sits below 50 CFS. At 107, you’re in a borderline zone—wading is manageable, but the river is compressed and transparent, and every fish has already clocked you before you’ve clocked the rise. More importantly, water temperature is holding at 57°F, which is cool enough to keep trout from full-blown heat stress, but the thin flow means thermal refugia—the deep slots and shaded cushions—are worth their weight in gold. Before you drive down, check the live flow chart on this page. These flows swing hard and fast on a tailwater controlled by dam releases; the 107 you see now might be 200 by midweek or down to 70 by Friday. Plan accordingly.
Fall BWOs and Midges: The Early-September Soft Hatch
September is when fall Baetis and midges reassert themselves after a summer lull. You’re not looking at a dramatic spinner fall or a blitz—this water doesn’t work that way in early fall. Instead, expect scattered to steady emergence of #20–22 BWOs on overcast afternoons, usually triggered by cloud cover or light. The hatch is real but technical: low light, thin water, and selective fish mean delicate presentation and smaller flies than many anglers bring.
Midges, however, are the constant underneath. Black Beauty, Mercury, and zebra midge patterns in #20–24 remain the daily bread on this tailwater. At 107 CFS with gin-clear water, trout have time to inspect every offering, so don’t skimp on tippet quality or leader length.
There’s also a tailwater quirk worth noting: terrestrials (ants, beetles, grasshoppers in #16–18) still pull fish hard into early September, especially where banks meet current seams and trout are feeding up in shallow slots. The insects are legit, and as water clears, visibility makes terrestrial presentations more attractive to trout that might otherwise ignore them under higher, off-color flows.
Reading the Water at This Flow
At 107 CFS, the river’s structure is compressed but highly organized. The main current tongue runs narrower and faster; the slack water behind boulders and in the inside bends is tighter and shallower. This is good news and bad news. Good: trout are concentrated and predictable—you know where to look. Bad: they’re also skittish and have nowhere to hide if your leader cracks over them or your fly lands like a brick.
The deep slots near the dam (where release flows funnel) remain the most reliable holding water. Trout stack there because the flow is consistent, the bottom is rocky and complex, and cooler water lingers. These narrow, darker seams are where your efforts should begin. The thin, sunlit flats—normally marginal in any flow—are nearly worthless now; skip them unless you spot active rising.
Undercut banks and any overhanging vegetation add value at low flow. Shade is temperature control; trout will position in or under shadows to stay cool. Look for willows or cottonwoods; fish tight to the bank if the current let’s you approach without spooking.
The Rig for Gin-Clear Water
Start with a 12-foot tapered leader, 5X butt, stepping down to 6X tippet for small dries and emerger dropper work. At this clarity and flow, 5X often feels fat; 6X is honest fishing.
For nymphing, the anchor fly needs to reach bottom in the deep slots. A Barr’s-style pattern in olive or black (#18–20) works: tied heavy or weighted, it sinks fast and stays in the zone. Add a single small split shot 8 to 10 inches up the leader to tick bottom without hanging constantly. Your dropper—the trailing fly—should be a #20–22 BWO emerger (Baetis nymph) or a small midge emerger (RS2 or Mercury in #22–24), tied 16 to 20 inches below the anchor. At low flow, the emerger often outfishes the point; trout rising to take insects in transition are eager and less critical.
Fish an indicator if you prefer it, but tight-line nymphing is often more effective in this water’s thin current. You feel the take earlier, your drag on the flies is minimal, and you can walk your flies down the seam with precision. Use a 3X or 4X indicator if you go that route; this water rewards contact and control.
For dry-fly moments (fall BWOs or terrestrials), use a 7X tippet if the fish are very selective and you’re confident in your knot work. If you’re new to long, fine leaders or the tippet is older than a season, stick with 6X—you’ll land more fish, and the performance difference in 57-degree water isn’t dramatic.
Where to Spend Your Time
The broken water around current seams—where the main tongue meets slower water—is the sweet spot at 107 CFS. These zones offer trout a choice: soft water to rest, hard water to feed and find food drifting. Work your way slowly through these transitions, focusing on the softer margin first. Cast upstream and slightly across, let the fly swing into the slack water, and watch for takes in the last three feet of the swing.
Deep runs and pools below modest boulder structures hold fish, especially if there’s an eddy or current shadow. These are the predictable lies at low flow, and they reward patience and good line control. One slow, careful drift through these pockets beats three sloppy passes.
Skip the wide, shallow flats between here and there. At 107 CFS on a clear day, those thin zones are temperature traps and exposure zones. Trout won’t loiter there unless they’re feeding on the surface, and surface activity at midday is sparse.
A Water-Temperature Note
At 57°F, you’re not in heat-stress territory—this water runs cold year-round, thanks to the dam—but the thin flow and September sun mean that afternoon water temps can drift upward by a few degrees. Carry a thermometer. If water climbs past 60°F, consider backing off active stripping and focusing on dead-drifts and subtle takes in deep, shaded water. Stop targeting trout in the thin flats once midday sun hits full strength; move to dusk instead.
Fish early and late in the day when the water is coolest and trout are feeding most confidently.
Check the live flow chart before you head down. At 107 CFS, this tailwater fishes, but it demands precision and respect for its transparency. Fall is here; the bugs are small and the window is tight. Come ready for 6X and long, delicate casts.