What does all this have to do with catching fish? Well, here are some useful observations, based on our fishing/entomological experience.

1) Baetis nymphs are strong swimmers. (The Baetidae family is generally referred to in entomological literature as "the small minnow" mayfly.) This means that motion imparted to a weighted nymph often does the trick. But don't just aimlessly swing your nymph imitation in the current. Also, don't make the mistake of weighting the nymph itself too heavily, thereby detracting from the motion naturally imparted by microcurrents around the fly.

Sulphur emerger

Use an unweighted #20 Pheasant-tail Nymph, with a #8 or #6 split-shot placed about 12 inches up from the fly and a strike indicator placed about three feet up from the fly. Cover the water with upstream casts and retrieve line at about the speed of the current. Every once in a while, but not on every cast, retrieve your line slightly faster than the current, but only by an inch or two when you think the fly is in the strike zone. This will cause the fly to pop up off the bottom in a downstream direction. The technique can be a killer during the prehatch period.

Small Pheasant-tail Nymph.

2) The abdomens of Baetis nymphs and duns are much narrower than those of the Ephemerella (PMD), which hatch earlier in the morning. If your Pheasant-tail Nymph patterns or your Compara-dun patterns have thick abdomens, as many store-bought flies do, you may as well leave them at home during the "Sulphur" (Baetis) hatch. A thin, olive Pheasant-tail Nymph or pale olive/pale yellow thorax dun, both in #20 or smaller, are well suited to matching this hatch.

3) The summer afternoon Baetis hatch occurs simultaneously with a Diptera (midge) hatch (about a #22). Unless you are willing to switch often between a mayfly nymph pattern and a midge pupa pattern, your success will be limited. Also, you must be willing to switch flies and/or tactics on any given fish.

4) Pay careful attention to riseforms. Many trout are dun-shy during the Baetis hatch, but will take nymphs just under the surface; you can see their backs "bulging" through the film. Inattentive anglers think the fish are feeding on surface-riding duns or floating nymphs, and they waste time using surface imitations.

John Mingo looks for trout sipping Baetis nymphs in the surface film.

No one knows for sure why the spring-creek trout are so reluctant to take duns during the Baetis hatch. Perhaps the fish are weary after a morning of taking dun imitations during the PMD hatch. Indeed, it seems that as August progresses and the morning PMD hatch wanes or disappears altogether, dun imitations become more effective during the afternoon Baetis hatch.

One of the most effective tactics for taking bulging fish during the Baetis hatch involves placing micro-indicators close to an unweighted nymph or pupa imitation. A #20 Pheasant-tail Nymph on 7X tippet with a micro-indicator placed 12 inches up from the fly can often do the trick. [For details on this method, see John Mingo's "Modern Spring Creek Tactics," Fly Fisherman, March 1993. The Editor.]

5) Finally, many fishermen make the mistake of staying in one place on the creeks for long periods of time. Our experience shows that after only three or four well-placed casts to a single fish, your chances of a hookup become exceedingly low unless you change flies, tactics, or targets. Switching between weighted nymphs, nymphs with micro-indicators, and floating emergers is all that is needed.

No Hackle baetis immitation.

Anglers who don't fish the Paradise Valley spring creeks regularly misjudge the number of fish in the streams and their distribution. During the summer Baetis hatches, the fish feed everywhere--almost every square yard of surface hides one or more fish eager to take a properly presented imitation.

Try to move around, even if you are constrained by other anglers upstream and downstream of your position. Often a change in position of less than 20 feet can make available several new target trout, or better anglers on existing targets. The best guides understand this and reposition their clients many times during the day.

We hope this rundown proves helpful. Have fun next time you are in the Livingston area, and don't forget to bring skinny flies and light tippets when the Baetis are hatching.

Also, consider donating to the Yellowstone Spring Creek Foundation. For more information or to make a tax-free donation, write to the Yellowstone Spring Creek Foundation, PO Box 8011, Livingston, Montana 59047.