Pteronarcys californica, commonly called salmonflies or willow flies, can provide the best dry-fly fishing of your life, or be the biggest let-down of your season. Most often, fly fishers walk away from the big hatch of those two-inch long stoneflies feeling less than content.

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However, nobody, from a flyshop owner, to a guide, to your fishing buddy, to a befuddled spouse--who just wanted to sit beside the river and read a book--would dismiss the merit of a salmonfly hatch. If you catch it on a good day, when those big stoneflies flutter through the air like failing helicopters, many of them crashing to the water to be greedily swallowed up like hot wings at a Super Bowl party, you'll never forget the experience.

On days like those, good fly fishers commonly land 20 to 40 mature trout a day--all on the surface. Even relatively inexperienced anglers enjoy hefty tallies; drag a fly across the surface, hang it on a bush and dangle it over the river, deposit it on the surface in front of your feet as you deal with a snarled mass of line on your reel, and a fish will sometimes eat it.

I ran into a situation like that on the Big Hole River two seasons ago, and I will never forget it. Every large trout in the river seemed to be up top, scarfing helpless adult salmonflies off the surface. Any bushy dry fly got pounded when I slapped it on the surface. By the end of the day, I thought I was some kind of angler.

What made that event so memorable, was all of that time I'd already spent on rivers during the salmonfly hatch paying my dues, and enduring such a frustrating time. The salmonfly hatch, which can be so easy to match when the fish are on, is a complete bust when conditions aren't just right.

Hatches of most other insects can be much more predictable and dependable. When PMDs are hatching for instance, it usually goes on for weeks, at pretty much the same time year after year. A salmonfly hatch progresses up a river a few miles each day, sometimes hastened by warm weather, sometimes slowed, or even halted for a short time by a cold front. Although trout may be caught over the length of the river, the hatch itself is only on a small portion of the river at a time, and only for a very short while--a couple of days at most.

Most anglers follow the hatch, choosing to fish where they see most of those winged adult insects in the air. If the trout gorge themselves too heavily on the adult insects, they often turn their attention to the bottom of a river where they can rest and digest. When they do that, they are likely to refuse your offerings, no matter how attractive your dry fly looks or how many real salmonflies are twitching on the surface. It's the only hatch I know of where the fish can actually get full.

To avoid the salmonfly saturation problem, you can move downstream where adult salmonflies haven't been present for a couple days and the trout are regaining an appetite, and still keyed-in on large dry flies. You may see only a few lagging adult salmonflies in the air, or maybe none at all, but the fish still recognize a bushy dry fly as an easy meal.

You can also move above the main hatch where trout are still in the process of gorging themselves on adults. They should also be actively feeding on big salmonfly nymphs that are moving into shallow water where they will drag themselves out of the water to dry their wings and commence mating and egg-laying flights--if they are not swallowed by a trout before they make their aqua-exodus. Under those circumstances, anglers can work large, weighted stonefly nymphs, such as a Kaufmann's black stone or a Bitch Creek Nymph, through the shallows or medium-depth runs and take fish

Hitting the salmonfly hatch "just right" has been difficult in the past, because it has been hard to know when and where to find the emerging insects, and good waters conditions, at the same time. By using Fly Fisherman On-line professional reports you can find out what is hot right now, pack your gear, and have the best fishing of your life tomorrow.

While there is always a chance you might hit a salmonfly hatch just right, as I was fortunate enough to do on the Big Hole River two seasons ago, most often the best fishing occurs ahead of or behind a hatch and that is where you should focus your angling effort.

If you want to catch a salmonfly hatch in the northern Rockies this year, there are lots of opportunities, beginning with the last few days of Pteronarcys californica action on western Montana's Rock Creek and upper Bitterroot River, plus eastern Idaho's Henry's Fork River. Here is a look at other salmonfly options in the northern Rockies, including their expected emergence dates.

Blackfoot River. The Blackfoot salmonfly emergence gets going a little later than nearby Rock Creek. Look for some action between June 1 and June 15. Densest salmonfly populations occur in the canyon section.

Gallatin River. Due to its elevation, the Gallatin salmonfly hatch doesn't heat up until mid-June at the earliest. Sometimes the hatch doesn't really perk until early July. When it comes off, try the canyon section, downstream from Big Sky, or throw a line upstream in Yellowstone National Park.

Big Hole River. Look for this emergence to begin around June 10, although any poor weather might push it back a few days. As mentioned, this emergence can be epic, but you'll have lots of company on the water. The emergence extends through the end of the month.

Firehole River (Yellowstone National Park). Typically an early-season hatch, look for salmonflies on this interesting trout stream during the first two weeks of June. PMDs and caddis should be present at the same time and they provide good options, too.

Yellowstone River. In the upper river, located within Yellowstone Park, look for salmonflies between July 15 and July 25. Downstream between Gardiner and Yankee Jim Canyon, expect them earlier, somewhere between June 20 and July 10. Between Yankee Jim and Emigrant they'll show up between July 15 and July 25. Between Emigrant and Mallard's Rest, expect them a little earlier, say June 25 to July 5. In the Livingston area, look for them between June 20 and July 5.

South Fork Snake River. If all fails and you don't hit salmonflies just right on any of the aforementioned rivers, the South Fork Snake can bail you out. Its salmonfly emergence, a good one, arrives in late June at the earliest, but usually comes off sometime in July. The river's cutthroats are less demanding than rainbows and browns found on other rivers and you can really stick it to them when you hit this hatch -- proficient anglers boast of 50-fish days.

While western salmonfly hatches can be maddening at times, they also provide some of the best big-fish/dry-fly options of the year. By fishing ahead of or behind the hatch you can lose those crowds of anglers associated with this emergence and you may tie into your largest fish of the year--trout over 20 inches aren't too shy to rise to a salmonfly dry!