In this report
260 CFS: Right in the Zone, But Water Temps Are the Limiting Factor This Week
The flow is sitting at 260 CFS — squarely inside the 250–400 ideal band for Cheesman Canyon and close to the 265–305 window where fish are genuinely spread through their summer holding water rather than compressed into the deepest slots. Wading is manageable, the granite-walled pocket water is fishing well, and you’re not battling a brown-water surge or stumbling over slick rocks in shin-deep current. This is genuinely good technical water.
But here’s the honest part: midsummer water temps on a tailwater releasing from depth are starting to matter, and you need to fish it with that in mind. The dam gives Chestream consistently cold water year-round — that’s the gift of this canyon — but the afternoon sun on those exposed granite walls and the overall seasonal warmth mean you’re looking at water temps creeping toward the high 50s to low 60s by mid-afternoon. That’s not dangerous yet, but it’s a clock on your fishing day. Start early, fish hard through the morning and into the early afternoon, and be thoughtful about how long you’re on the water if it’s been hot.
PMDs, Midges, and Small Caddis — the July Sequence
The primary driver right now is the Pale Morning Dun hatch, which runs through midsummer on this tailwater in #16–18 sizes. You’ll see genuine emergences in the flatter, slower-current seams — the glassy water between and downstream of the big boulder fields — typically from mid-morning into early afternoon. The emergers are often more productive than the duns themselves; fish are keyed on the nymphs and the half-drowned transitions, not the fully dry fly that floats past in clear water.
Underneath and concurrent with the PMD action, midges are the real backbone of this canyon’s diet year-round. #20–24 patterns — Zebra Midges, Mercury Midges, Black Beauties, RS2 emergers — should be on your rig constantly. On Cheesman’s educated trout, the midge is often the deeper anchor fly in a tandem setup, and it produces steadily through the day regardless of visible hatch activity.
As afternoon advances and water temps climb, small caddis (#16–18) start to show in the evening hours. Nothing explosive — this is not a freestone caddis blow — but enough to bring trout off the bottom and get them looking up. You’ll also see terrestrials (small ants, beetles) take a role on warm, windless afternoons when hoppers aren’t really dominant yet; keep #14–16 patterns on the box as an occasional dropper or sight-fish option if you spot risers in the slower edges.
The Rig: Anchor Heavy, Dance Light
At 260 CFS and this time of year, the classic Cheesman small-fly, light-tippet approach is the framework, but your exact setup depends on whether you’re fishing the faster-pocket water or the slower seams.
For the pocket water and faster runs (the character you’ll encounter most on the hike in — tight, boulder-strewn channels where current is constant and holding water is defined by depth rather than slack):
Use a heavier midge as your point fly — a #20–22 Barr’s Tungsten Midge or Mercury Midge with a bit of weight — and add a single split shot approximately 18 inches above it. This anchor gets you to the bottom quickly and lets you feel the substrate. Tie a 12-inch dropper 18–24 inches above the split shot and hang a #18 PMD emerger or lighter #20 midge there. Fish it on a tight line or with a small yarn indicator depending on your feel for the water. Use 4X or 5X to the midge and 5X to the dropper — the lighter stuff is critical in this gin-clear water, and 5X will break off less than you think if you’re patient on the hookset.
The goal is to be bouncing the bottom fly and suspending the emerger just above it. On a 260-flow day with solid depth in these slots, that’s your bread-and-butter approach for the technical stuff. Fish it methodically — tight-line or indicator, your choice — and count down to let that split-shot anchor settle.
For the slower seams, glassy water, and the rare flat-ish run (you’ll find these in the canyon, usually between boulder clusters where current slows or pooling occurs):
Scale down further. A single #20–22 Zebra or RS2 as a point, no split shot, with a 15-inch dropper of #18 PMD emerger above it on 5X tippet. Fish it under a small indicator set 4–5 feet above the flies, or switch to a tight-line nymphing presentation if the water is shallow enough that you can sense the bottom without weight. These glassy pockets are where the truly spooky, large trout live, and they’ll see a split shot coming a mile away.
Never overload the indicator approach in this canyon’s pocket water — the trout are wild, the water is clear, and a yarn indicator can spook a fish 20 feet away if it lands hard. Dry-drop or tight-line when you can; indicator when depth or current demands it.
Water Types Worth Your Time
The fast, boulder-choked channels are the engine of this canyon. Fish them with rhythm — cover ground, work every transition where current slows around a rock, stay in the deeper slots where the water darkens. That’s where concentrations of holdover trout live, and at 260 CFS, they’re spread and feeding, not compressed into a handful of desperation lies.
The slower glassy runs between boulder fields deserve longer, more deliberate presentations. These are where you’ll find the largest, most educated fish, and they’ll reject poor drifts and heavily-dragging flies instantly. Make fewer casts, but make them count.
Avoid the super-shallow, gin-clear riffles where depth is only 1–2 feet unless you have a sightfishing opportunity. The trout will be there, but they’re hyper-alert in thin water, and you’ll spook them before you fool them.
Hike Timing and Stewardship
The canyon’s 1.3-mile hike in from the Gill Trail is the only access, and at current water temps creeping into the low 60s, you’ll want to maximize daylight and minimize midday crowding. Start early, be off the water by mid-to-late afternoon, and give those fish a temperature break. If this week turns particularly warm, consider shifting your session to early morning only rather than an all-day push — the trout in this tailwater are resilient, but they’re not indestructible, and Cheesman’s small size means your impact is magnified.
Catch-and-release on this water is non-negotiable and has been since its inception. Handle fish quickly, keep them in the water, and if you’re taking photos, make them fast.
260 CFS is honest, fishable water. Fish the midge-and-emerger combination, respect the clarity and the education of these trout, and you’ll have a technical, rewarding day. The hike is real; plan for it, start early, and don’t overstay as temps climb.