Rio Grande and San Juan trout settle into fall pattern

What's biting

What's next

With a New Moon, the night sky is dark and early mornings are the cleanest window. Water at 66°F typically sits at the upper edge of comfortable for Rainbow Trout and Brown Trout, so plan to be on the water at first light and wrap up by late morning, when the warmest part of the day pushes temperatures higher. If nights keep cooling, readings at 08317400 should drift down and the bite should stretch later into the day.

Flows matter as much as temperature. Moderate flows like these generally keep fish in seams, soft edges and the tails of runs rather than spread across the main current. Per Gink and Gasoline (fly), adding enough weight to a tandem nymph rig is often the difference between getting bites and not, so check that your flies are reaching the strike zone. Trout Unlimited likewise notes that weight matters when nymphing. Small olive and midge patterns are a sensible starting point, in line with what Reno Fly Shop (NV) suggests for fall.

Watch the gauges before you drive. A jump in flow at either site would change where fish hold and how deep you need to fish, and a steady drop in temperature is the signal that the afternoon bite is coming back.

Context

Mid October is typically the shift from summer to fall patterns on southwestern rivers. Water that ran warm through summer starts to cool, hatches of small mayflies and midges become more important, and fish that were sluggish in the heat feed more consistently. Brown Trout also begin moving toward their fall spawning phase in many systems, so check local regulations and avoid wading through spawning gravel.