In this report
Flow Is Below Par—Check Before You Go
Before you load the truck, pull up the flow chart on this page. Eleven Mile has been running thin for early August, and if the gauge is holding below 100 CFS, you’re looking at a week where wading is easier but fish are spookier and holding tighter to structure than usual. This tailwater’s typical summer range sits 50–150 CFS; anything under 75 CFS puts you in the lower quartile, which means the pocket water that usually holds pods of willing fish shrinks noticeably, and the runs flatten. The good news: low flow makes spotting fish easier and puts them in predictable lies. The hard news: they see you sooner, and with less water to hide in, your approach matters more than it does when the river’s running fuller.
If the gauge shows 100–120 CFS, you’re in workable territory—low but not alarming. Above 150 CFS and you’re moving toward that ideal dry-fly band. If it’s nudged over 200 CFS, the canyon’s pocket water gets more complex and rewarding, but you’ll still have good wading. Anything over 300 CFS and the tight-line nymphing that defines Eleven Mile gets frustrating fast.
Check the flow before you leave. Don’t guess.
Midges Dominate; PMDs Are Fading
Early August means the Pale Morning Dune hatch is tapering off even as terrestrial season ramps up. Don’t lead with PMDs—that’s a June and early July story. Right now, the season’s primary pattern is midges, and on a confined tailwater 3.8 miles long with pocket water and small holding zones, midges are your bread and butter.
Fish #20–24 midge emergers on the nymph side: Black Beauty, Mercury Midge, and zebra midge in cream or olive. These are thin-bodied, realistic, and they work because the South Platte below the dam is a consistent midge-factory year-round. Tie them on 6X and 7X tippet—these flies are small enough that fine tippet is both necessary and honest. An RS2 emerger works equally well and fishes similarly.
Tricos (#20–24 spinners) will show in the morning hours, especially between sunrise and 10 a.m. if the weather stays warm and the air is calm. They’re not a dominant hatch here the way they are on the Dream Stream, but they’re present enough that a small spinner pattern is worth having in your box. The spinner fall is brief, so if you see rising fish in that window, switch immediately.
Caddis will tick up in the evening—nothing like a freestone, but present enough to warrant a small tan or olive caddis pupa (#16–18) in your dropper position as afternoon temperatures peak. August afternoons on this narrow canyon can push water temps up noticeably by 4 p.m., so fish early and late when you can.
The Rig That Works This Week
Low flow means tight-line nymphing is your primary tactic. Forget the indicator unless you’re fishing the deeper pools near the dam; the water’s too shallow and the currents too predictable for indicator work to be worth the hassle.
Tie a heavier anchor fly—a #18 Barr’s Graphic or similar tungsten-heavy nymph—to your 4X or 5X main tippet. Two feet above that, drop back to 5X and attach a #20–22 midge emerger or RS2. This setup lets you dead-drift the anchor through the pocket water, feeling the ticks on bottom, while the smaller emerger trails just below it where feeding fish are actually looking. At low flows, that trailing fly is often the one that gets hit.
Add a single small split shot—#8 or smaller—pinched onto the tippet 18 inches above the anchor. You don’t need much weight; the goal is to tick the bottom of the deep slots and the soft seams between rocks without tying you up every third cast. If you’re snagging constantly, you’re overdressed.
Use 4X as your main tippet. In low, clear water with spooky fish, that feels like overkill—and you might could get away with 5X—but the canyon’s proximity to the road means occasional wade-by disturbance is real, and heavier tippet buys you insurance on a good fish without sacrificing takes on small flies.
Where the Fish Actually Are
In low flow, forget about the broad runs and open banks. Fish are in the deeper pockets and the tight seams where rocks funnel current. That character doesn’t change week to week, but it becomes tactically critical when the water’s down: the small soft-edges and behind-boulder slots that hold a few fish in higher flow become the only holding water now.
Wade deliberately and fish the near bank first—the canyon’s roadside proximity means the far bank gets pressure, and low water makes spooking fish from your own side a genuine risk if you’re not careful. Work from downstream of your target pocket and approach at a low angle. With less water to hide in, even the trout that aren’t looking at you directly will bolt if they sense a shadow or vibration.
The pools immediately below and adjacent to the dam are spring-fed and slightly cooler; if afternoon temps are climbing above 65 degrees, start there rather than working downstream into the warmer runs.
Water Temperature and Fish Welfare
August tailwater temperatures on the South Platte can spike fast once mid-day sun heats the surface. If the thermometer touches 67–68 degrees, ease off the deeper fishing and concentrate on shaded, pocket-water zones. Eleven Mile’s narrow canyon means shade is more plentiful than it is on open freestones, which is a genuine advantage in warm weather. Use that.
Keep your hands wet if you must handle a fish. At low flows and warm temps, stress compounds quickly. Quick release and minimal air exposure are not optional.
Access and Logistics
The $11 day-use fee is a US Forest Service charge—your state parks pass won’t cover it. The Quality Waters section runs 3.8 miles from the dam down to the Wagon Tongue Gulch bridge. The road is pullout-accessible, so you can park and fish without scrambling down cliffs or portaging gear. That’s a defining feature of this canyon and a genuine convenience, especially if you’re scouting new water or limiting your walk.
The old railroad bed makes for an easyish road walk between spots, though the canyon narrows in places. Wear good boots and bring water.
Get on the water early. Low flow, warm sun, and proximity to a paved road all favor an early start. By mid-afternoon, both fishing and fish welfare decline.