Beginning in late June or early July the prime hatch on this river occurs—salmonflies! There are few hatches that excite anglers as much as the salmon fly hatch. Visiting anglers will plan a year in advance and book guides and lodging over a two weeks span to “hit it” right and local anglers will leave their day jobs at a moment’s notice to be on the water.
Why is the salmon fly hatch so exciting? For starters it is the first major hatch on the Yellowstone in nearly a month, the river is finally clear enough to fish, and the insects themselves are nearly three inches long! For some bass anglers or folks used to fishing plugs and jigs a three inch fly or bait may not seem that large. However, keep in mind that most trout eat small insects and most trout do the bulk of their feeding under the surface out of sight of most anglers. When a trout rises to the surface to eat a dry fly that is nearly a quarter of a foot in length, it is very exciting. Add to that drama the principle that big fish eat big flies and if the biggest food source is floating along surface instead of crawling along the bottom, that equals big fish eating big flies on the surface creating sight that is rarely seen on most trout streams.
Because rivers run from cooler areas to warmer areas the salmon fly hatch actually moves upstream as the water temperatures rise. The sections of the river where the insects are hatching (or flying around and landing on the water) follow a gradual upstream pattern at a rate, in most years, of about three miles a day. Because the hatch moves upstream and the good fishing water on the Yellowstone is nearly 150 the hatch will last for a considerably long timeframe. The kicker in most years: does the river clear enough to the fish can see these big flies! And that fact is one of the main reasons the hatch is such a fun hatch to fish because some years the river is clear enough to fish and other years the bugs are everywhere and the fish are not rising in the muddy water.
Once the excitement of the salmon fly hatch subsides and the bugs are no longer to be found, another large insect emerges, the golden stonefly. In the same biological family as the salmon fly, the golden stonefly is about an inch to two inches in length and still a large morsel for trout to pick off the surface. Like their larger predecessor these bugs tend to hatch off of bankside vegetation so anglers will target similar water.
Other late June and early July hatches to be on the lookout for are Yellow Sallies, a smaller stonefly, and green Drakes, a large mayfly often found in Montana freestones.
Moving later in July and into August the Yellowstone’s main hatches are caddis and tricos in the early morning and caddis again in evening. However, the Yellowstone’s trout diligently look for hoppers, ants, and beetles more so than caddis and tricos. Up until the increased fishing pressure of the past ten or so years the hopper fishing on the Yellowstone used to be so good that when a guide would tie on a new grasshopper pattern onto the end of the leader of one of his or hers client’s rigs and then toss the fly out and over the edge of the boat, before the client could cast again he would yell “set!” because a fish would strike that quickly.