South Platte Running 110 CFS as May Hatch Season Opens on CO Tailwaters

What's Biting

What's Next

**Next 2–3 Days: Monitor Flows and Target the Hatch Window**

At 110 cfs, the South Platte is in comfortable territory for wading most standard access points — riffles, tailouts, and pocket water that concentrate fish are all accessible at this level. Early May sits at the edge of runoff season, however, and upstream snowmelt or reservoir releases can push levels up quickly. Check USGS gauge 06701900 the morning you plan to fish; flows climbing toward 200 cfs or beyond typically make wading difficult at many traditional access points and push trout into edgier, harder-to-read lies.

No water temperature data was captured on this reporting cycle. Typical South Platte and Arkansas tailwater temps in early May sit in the low-to-mid 50s°F range — near the metabolic sweet spot for trout. Fish activity should build progressively as surface temps warm through the morning hours, with the best dry-fly window opening between roughly 10 a.m. and 2 p.m.

With the Full Moon just cresting, concentrate effort around low-light windows. Arrive at legal light and plan to stay through mid-morning. Field & Stream's current guide to aquatic insects for trout identifies mayflies and midges as the bedrock of tailwater trout diets — a #18–22 Parachute BWO or Comparadun fished on 6x tippet through slower seams is the standard mid-morning approach. A midge pupa dropper under a small indicator handles the subsurface window during the cold early hours before surface activity materializes.

Afternoon sessions may begin to show early-season caddis — an Elk Hair Caddis (#16) swung or skated through riffles after midday is worth cycling through as light drops off the water. Evening windows will extend as May progresses, making late-afternoon-to-close sessions increasingly viable heading into next week.

On the Arkansas tailwater, flow data was not captured for this cycle. Hatch timing there typically tracks within a day or two of the South Platte — if BWO activity is producing on one drainage, expect comparable insect emergence on the other.

Context

No Colorado tailwater-specific angler reports appeared in the intel feeds this cycle — the historical context here draws on typical early-May patterns for this region rather than sourced testimony.

For the South Platte and Arkansas tailwaters, early May historically marks the shoulder between the winter-into-spring midge season and the onset of snowmelt runoff. Below-dam tailwaters hold their fishability through this transition longer than freestone streams because regulated reservoir releases buffer against sudden temperature and flow swings. In most years, flows begin climbing toward runoff levels between mid-May and early June; the 110 cfs reading this morning suggests we are still comfortably in the pre-runoff window — historically one of the best dry-fly periods on these drainages. Fish are well-conditioned after months of stable tailwater temperatures and tend to respond more readily to emerging insects now than at any other point in the calendar year.

Full Moon conditions in early May historically coincide with productive BWO emergence. These mayflies are light-sensitive and tend to hatch under lower-light conditions — mornings and overcast afternoons — rather than during bright midday sun. Expect fish to distribute across the water column during full daylight and key to feeding lanes as light softens.

Field & Stream's current trout-insect primer provides a useful seasonal map for the weeks ahead: on Colorado tailwaters, midges and BWOs are historically the dominant patterns through late spring, with caddis becoming increasingly important through May and June as water temperatures climb toward the 60s°F. No corroborating on-the-water reports from charter, tackle-shop, or state-agency sources were available for Colorado tailwaters in this reporting cycle.