Montana Rivers


What to Expect in May

Note: This What-To-Expect is from Westfly's Legacy pages and may not accurately reflect the current fishing at this venue.

Usually, cool weather and warm weather play cat-and-mouse with each for most of May, which can leave rivers blown-out some of the time, and fishable at other times. When rivers get a brief respite from runoff-- high and colored, but fishable for short periods--they will be best fished with nymphs on the bottom and with streamers. Under these conditions, the most productive water will be near the bank.

Trout will be taking drifting salmonfly and golden stonefly nymphs on rivers that host populations of these mega-sized insects. San Juan Worms are another good subsurface option.

In all cases, get your fly to the bottom. Spilt shot, beadhead, extra weight under the body dubbing--whatever it takes and is still legal. If you aren't losing a few nymphs, you're not doing it right.

If there is an extended cool spell that slows down the effects of runoff--or if a spell of warm, rainy water hastens runoff and ends it before Memorial Day--topwater action can return.

In general, though, this is a month when you check the river levels every day. When you see an opportunity, go for it; it won't last.

Even when most rivers are high and chocolate brown, there are some tailwater fisheries and a few tributaries that remain fishable. Or you can head for a lake.

By mid-month, adult salmonflies will start to hatch. The nymphs crawl to shore; once the nymph is out of the water, the adult emerges, dries its wings, and flies to an alder tree where it utters the insect equivalent of "Hey, Baby, Baby." In their relentless pursuit of the opposite sex, adult stoneflies often fall or are blown out of the trees, land in the water, and are devoured by trout.

So if you cast a MacSalmon, Clarks Stonefly, Low Ball Stonefly, or Stimulator near shore and just downstream or downwind from overhanging vegetation--especially in the afternoon when the bugs and the wind are at their most active--you may catch a fish.

Note that just because the adult salmonflies are out, it doesn't mean trout are taking them yet. Trout are creatures of habit and can be slow to make the switch from nymphs to adults.

One hint: if you buy your salmonfly flies, buy them early in May because the fly shops only stock-up once and won't re-order until next year. If you wait too long all you'll find are empty bins or flies that are the wrong size, pattern, etc.

By late May the green drake nymphs will be on the move. Hatches of this large insect usually occur in early afternoon and probably won't begin until June. But the nymphs are usually active by late May, and trout will be on them. A Poxyback Green Drake nymph can catch fish when drifted through a run with a slow to moderate current. This fly has a shiny back, based on the fact that top of the thorax of most mayflies gets shiny just as it is ready to emerge.

March browns and pale morning duns are other mayflies you may encounter this month.

Grannoms (genus Brachycentrus), the "Mother's Day Caddis," are important on many Montana rivers. Hatches usually begin around mid-May, plus or minus a week depending on the weather. If the rivers are fishable at that time, use a Sparkle Pupa or Deep Sparkle Pupa with a green body and a tan shroud before and during the hatch. Dead drift it near the bottom, then let it swing up to the surface. If you see trout feeding consistently just subsurface or making splashy rises, cast a Sparkle Pupa upstream-and-across and let it drift drag-free just under the surface. See below for the color and size of adults.

Other active caddis species at this time of year are green caddis (genus Rhyacophila), spotted caddis (genus Hydropsyche), and saddle-case caddis (genus Glossosoma).

With caddis fly patterns, "close" is usually good enough, so you only need a couple of fly patterns; just vary the color and size to match the natural insects. For a dry, use an Elk Hair Caddis, Deer Hair Caddis, Casanova Caddis, X Caddis, or similar pattern.

Many caddis species lay eggs by swimming or crawling underwater, and they are often taken by trout. Use a wet fly such as a Soft Hackle or a Diving Caddis in the sizes listed above for adults; caddis get darker when ready to lay eggs, so use darker versions of the listed colors.

Blue-winged olives will hatch on many rivers, with the best hatches on cloudy days. Teaming a nymph with a large stonefly nymph will be a good strategy when there's no hatch. March browns may hatch on some streams, and gray drakes are present on some western Montana waters. Midges are also common on many streams this month.

Trout have been spawning in Montana rivers, so if you're wading over gravelly areas or see small rocky spots that are "cleaner" than their surroundings, you're probably on a redd. Get off it, and don't fish in that area. Spawners need their rest.

During runoff season the small streams will be the first to clear. Most small streams open the third Saturday in May.


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