In this report
Flow is Low and Rising Slightly—Fish Are Concentrated and Spooky
At 191 CFS, Cheesman is running well below the ideal 250–400 range this week, and that single number reshapes every tactical decision you’ll make on the canyon. The good news: the flow is stable and the gauge shows a slight upward trend. The hard truth: you are fishing for educated, concentrated trout in a canyon where their holding options are already limited by the granite architecture, and low water has compressed them further into the deepest slots and behind the largest boulders.
This is not a week to charge into the canyon expecting relaxed fish. The holding water that spreads nicely at 265–305 CFS is now consolidated. Every trout that holds a lie is aware of it, and the reduced surface disturbance means your fly line, your footfalls on the rocks, and your shadow travel farther and spook easier. This is the technical work Cheesman was built on—small flies, light tippet, long leaders, and the discipline to fish slowly and methodically. If you’re coming down the Gill Trail expecting 2024 conditions, reset your expectations now.
Midges Dominate; Morning Tricos Are Secondary
At this flow and water temperature (which at low summer flow tends toward the mid-50s in the upper canyon, cooling as you descend), the primary insect story is midges—they always are on this tailwater, and low flow makes them even more dominant. A #20–22 Mercury Midge or Black Beauty nymph under an indicator is your bread-and-butter search pattern, fished dead-drift through the deepest slots where trout are stacked tighter than usual.
Trico spinners are still happening in the early morning window (roughly 7:00 to 9:00 a.m.), and if you can time your hike to arrive just after dawn, the spinner fall on the slower, deeper runs can be productive with small #20–24 dry-and-dropper rigs or a pure small spinner pattern. But the window is narrow and tight—by mid-morning, the rise is over, and you’re back to subsurface work.
PMDs are still present (#18, occasionally #16), and the emerger phase matters here: a #18 PMD emerger fished as a dropper 16–20 inches behind a heavier anchor fly (a Barr’s Olive or similar) can take fish even in this low flow, because the emerger hangs just slightly off-bottom and moves like a natural ascending, rather than bumping and dislodging rock. Evening (last two hours before dark) is the PMD window—faster current that may not exist in your canyon that day, but still worth a swing through the faster boulder-pocket water with a small dry or emerging pattern if the light and temperature align.
Terrestrials are a real part of August, but at 191 CFS, keep them small and specific: a #16 black ant or small foam-bodied hopper in the slower margins and behind the biggest granite blocks, not as a search fly but as a sight-fish tool when you see a good fish holding shallow.
Rigging for Concentration and Spook-Avoidance
Your leader and tippet are where this week’s difficulty lives. Go long: 12–14 feet total leader, 4X or 5X tippet depending on fly size and the water type you’re fishing. The low flow means no noise cover, and the concentrated, aware fish demand a delicate presentation.
The working rig this week: Start with a #20–22 Mercury Midge or small dark nymph as your anchor (this is where weight lives; you’ll add 1–2 small split shot 8–10 inches above it to reach the bottom quickly without overshooting). Tie a #18 PMD emerger or a #20 Trico nymph as your dropper, 16–18 inches above the point fly, using a small surgeon’s knot or loop-to-loop connection. This lets you cover two zones at once: the nymph is searching for whatever is on the bottom, and the emerger gives fish a realistic ascending-bug option if they’re keying on emergers in the film or just above it.
Indicator: Use a small, sensitive one—a #2 or #3 pencil indicator, or a pinch-on foam bit in bright orange or yellow. At 191 CFS, you need to feel every micro-tick, because these fish are finicky and the low flow means less aggressive takes. Set up a dead-drift down the columns of deeper water, and be ready to strip-set on anything that feels wrong (stalling, sideways movement, hesitation). Don’t wait for a dramatic rise—confidence and quick reflexes matter more when the flow is thin.
Tight-line nymphing (euro nymphing) is also deadly here if you’re practiced with it: a slightly heavier anchor fly (size #14 nymph or small heavily-weighted Barr’s), tippet 5X, no indicator, and a leader that lets you maintain feel and constant contact. This method excels in the tight, complex boulder pockets where an indicator can snag, and it lets you fish shallower than depth-and-indicator rigs allow.
Fish the Deep Slots and Behind the Granite Armor
At 191 CFS, forget about the soft water along the banks. Trout are in two places: the deepest slots between and below the giant boulders that define the canyon, and in the shadow water directly behind—where the current breaks and creates a small refuge just below a rock face. These are your only worth-fishing targets right now.
Approach slowly, crouch low, and work each slot methodically from the downstream side. The canyon’s steep terrain and chaos of giant rocks mean you’ll do most of your wading blind or semi-blind—feel for the best footing, and trust the canyon’s architecture to hide you as much as it hides the fish. Cast upstream and slightly across, let the nymph tick the bottom through the deepest part of the run, and repeat 3–5 times per spot before moving on. Patience and precision beat coverage and speed.
The faster pocket water that might be fun at 300 CFS is mostly marginally worth fishing at 191; skip it in favor of the deeper pools and holds.
Water Temp and Fish Stress: A Real Stewardship Consideration
Low summer flow + mid-August heat = slower water speed and warmer pockets, especially as you move downstream through the canyon. Water temperature will creep above 55–56 degrees in the slower sections, particularly in the afternoons. Trout are manageable (not yet in acute stress), but they are less resilient. Play fish quickly and keep them out of the water for as little time as possible. If you catch and release, do so gently—a barbless hook (required on catch-and-release water) is both a regulation and a mercy at this time of year.
Consider starting your hike earlier in the day and winding down by early afternoon, rather than pushing into the warm hours. The morning spinner fall and the cool early-evening rise window are when the fish are most active and the water is coolest anyway.
The Hike, the Rocks, and the Reward
The Gill Trail is steep and technical, especially in sections where it narrows among the giant boulders. Wear good boots with ankle support and tread carefully on the granite—wet or dry, it’s slick. At 191 CFS, the canyon mouth (roughly 1 mile in from the Cheesman Canyon Trailhead) is accessible without technical scrambling, and the pocket water all the way through is fishable. Pack light (your rods, small fly box, minimal gear), bring water, and plan to spend 3–4 hours actually fishing rather than 6–7—the low flow rewards focus and precision over long hours.
This is Cheesman at its most demanding and most honest: a small tailwater where every cast matters because the fish are concentrated, aware, and not interested in mistakes. It’s why the canyon earned its reputation. Come prepared, fish small, and fish slow.