Weekly Hatch Report: Trumbull Section (South Platte — Below Cheesman to Deckers)

The South Platte below Cheesman is running clear and moderate for early May. Since live USGS data isn’t available this week, dial in the current flow at the Deckers gauge before you load the truck—this section’s character changes dramatically between 300 and 800 CFS, and May can swing both directions depending on snowmelt timing and releases from Cheesman Dam. At moderate flows, you’re looking at fishable water with defined seams and accessible holding zones. High water pushes fish tight to the banks and makes nymphing the slot work. Low flows compress everything into the deeper runs and require precision casting.

What’s Hatching

Early May on the Trumbull means you’re in the transition from spring blacks to summer mayfly populations. Expect overlapping hatches.

Blue-winged olives are still coming off, especially in the afternoons when water temps dip below 50 degrees. Size 18–20 Parachute Adams or Olive Sparkle Duns are your call. These aren’t massive emergences, but consistent enough that a few rises will materialize if you’re watching the right water between 2 and 4 p.m.

Little brown stoneflies (LBS) nymphs are active. You’ll want a Little Brown Stonefly Nymph in a 14 or 16, dead-drifted tight along banks where current slows. This is workhorse water—not fancy, but it produces consistently on a 5x or 6x tippet.

Baetis are still viable, especially on overcast days. Smaller populations than spring, but RS2s in 18–20 and Pheasant Tail Nymphs in 16–18 will connect.

Caddisfly larvae are ramping up heading into late May. The Trumbull has good caddis populations. A Tungsten Caddis Larva in tan or olive, sizes 14–16, fished on the bottom in current seams will draw strikes all day. This isn’t a hatch you’re matching; it’s a natural food source trout are keying on.

The big story is aquatic terrestrials—early season ants and beetles are falling in from riparian vegetation as you move downstream. Small black Carpenter Ant patterns (size 18) or a Foam Beetle (16–18) will catch opportunistic fish, especially along undercut banks.

Best Beats

The Meadow Run (mile marker 2–3 from Cheesman) is prime early May water. This section has lateral depth changes and willows that create wind breaks and terrestrial input. In moderate flow, the slightly slower water along the eastern bank holds resident browns that aren’t interested in chasing fast water. Fish the edge between the current seam and the slower water with a dry-dropper setup: a size 16 Stimulator or Elk Hair Caddis as the indicator, with a Tungsten Caddis Larva or Pheasant Tail 18 inches below. This beat is especially good if flow is running 400–600 CFS—it becomes too pushy above that, and less productive below.

Cheesman Tailings (mile marker 4–5) is a classic early-season hold. The residual dam structure creates complex current patterns and holding zones. Larger fish winter-over here and are actively feeding in May. Focus on the deeper inside bends and the slack water behind the old structure. A Copper John or Pheasant Tail in a 16, weighted appropriately for the flow, dead-drifted through the tailings section will connect with fish 14–18 inches. Use a 5x tippet; these trout are selective but not dainty.

What flies are working on the Trumbull right now?

Keep it simple: a Tungsten Caddis Larva (tan or olive, 14–16) and a Pheasant Tail (16–18) cover most of the subsurface work, with RS2s in 18–20 for the Baetis days. Up top, a Stimulator or Elk Hair Caddis as a dry-dropper indicator, and small ant and beetle patterns along the undercut banks.

Lower Monument Run (mile marker 6–7) is your option if the upper sections are crowded or if flows have pushed higher. Monument is slightly warmer and has more gradient, so afternoon hatches tend to be heavier here. The run has good dry-fly potential with Stimulator patterns, and subsurface work with small nymphs produces steadily. This section rarely gets as much pressure as Meadow or Tailings, and that translates to opportunity.

Tactics

Set yourself up with a 9-foot 5x fluorocarbon leader tapered to 5x or 6x tippet. The Trumbull’s water is clear; light tippet is non-negotiable, but the trout here aren’t leader-shy if you’re fishing small patterns and using proper presentation.

Go dry-dropper: a buoyant dry (Stimulator, Parachute Adams, Elk Hair Caddis) as your indicator, with an 18–24 inch dropper of 6x tippet tied via a surgeon’s knot or triple surgeon’s. Run a single nymph on the dropper—a Pheasant Tail, Copper John, or Tungsten Caddis Larva. This setup lets you cover two zones, match both surface and subsurface activity, and use the dry as a visual reference for takes below the surface.

Dead-drift nymphs along current seams and under overhanging vegetation. Strip slightly between drifts to trigger takes from aggressive fish, but don’t abuse it—this section rewards precision more than activity.

Practical Notes

Cell service is spotty on the Trumbull, especially down-canyon. Download your maps before you head out. Know where parking is before dark; turnouts fill on weekends.

Water temperature is a variable worth tracking. Early May means the water can range 44–52 degrees depending on time of day and cloud cover. Warmer afternoons will trigger more surface activity and faster nymph feeding. Fish accordingly—slower presentations in cool mornings, more aggressive fishing after 1 p.m.