Idaho Rivers

HATCH

NYMPH/
LARVA

PUPA/
EMERGER

DUN/
ADULT

EGG-
LAYER

Blue-winged olive

Mahogany dun

Trico

October caddis

Green caddis

Golden stonefly

Salmonfly

Cranefly

Midge

Sculpin

Hopper

Crayfish

Baitfish

Beetle

Ant

August may have been hot or cool, dry or damp, with good or ill effects on the fishing. But things change in September--almost always for the better. There's just nothing we can do about the earth's changing tilt toward the sun. September brings cooler, longer nights, and that sparks a revival of hatches and great fishing. We should see some rain, too, and it will be welcomed by all.

Many areas will begin to see frost at night, especially later in the month. That will knock back the tricos and hoppers. Caddis will still be important this month, but after six weeks of the hopper-dropper-trico-caddis mantra, two mayflies return to prominence in September: mahogany duns and blue-winged olives. In rivers with brown trout, big streamers will become increasingly important as the month progresses and the browns become aggressive.

The mahogany duns (Paraleptophelbia) create trout feeding activity in quiet bankwater because that's where the nymphs migrate before hatching. If you see trout languidly rising in slow water near the riverbank this month, you're probably witnessing a mahogany dun hatch. DON'T cast blindly. In this quiet water you'll spook the fish. Instead, watch the rises and pick a single trout. Use a downstream presentation so the fly reaches the fish before the leader and line.

The other mayfly that returns this month is the blue-winged olive. Hatches will be sporadic, but nymphs are active and are taken by trout more regularly than the duns, especially in riffly water; see A Little Known Two-Fer-One for tips on how to take advantage of this.

October caddis may show up by the end of the month. Trout take pupa patterns as well as adults. When fishing an adult October caddis pattern, you'll probably catch more trout if you skate the fly across the surface than if you dead-drift it.

Salmonfly and golden stonefly nymphs, which are never totally off the menu for trout, will become more important this month. Two-nymph rigs, with a big stonefly nymph on the point, will be very productive when no hatches are in progress.

Steelhead are a big item for many Idaho anglers. It will be better in October, but this month you'll find fish heading into the Clearwater and lower Salmon when the water temperature of those rivers is lower than the Snake. If the river flow drops and the water warms up, those steelhead will move back into the Snake.