April and May Hatches On The Yellowstone River: Spring Fly Fishing in Montana at its Best

Spring scenery in Paradise Valley

Spring is unquestionably the most underrated time of year to fish the Yellowstone River. As water temperatures rise, the trouts’ metabolism begins to increase, putting them on the hunt for food. Fishing pressure is low during spring, and most trout on the ‘Stone haven’t seen a fly in months. While nymph fishing is very productive in the early season, it comes as a surprise to many that spring is a actually a great time to dry fly fish.  The big stonefly hatches of early summer garner the most fame, but a strong argument could be made that the years best hatches go off in April and May. The bugs come every year and the fish will be hungry, so water clarity is the only variable. The Yellowstone will come in and out of fishable shape several times each spring, as warm weather begins to melt the low elevation snowpack and cool weather locks it back up. Fortunately, we are blessed with many other great fishing options in the spring as we wait for the ‘Stone to shape back up. Let’s take a look at the 3 major hatches that get the trout looking up each year.
Blue Winged Olive's are the first major hatch of the year on the Yellowstone River
Blue Winged Olives
The BWO’s, or Baetis, are the first major hatch of the year. These small, dark colored mayflies typically begin to emerge in earnest in late March or early April. The hatch will persist into early May, especially on cool, cloudy days. The hatch typically comes off around lunchtime and lasts through the warmest part of the day. Sunny days will see scattered rises throughout the river, but on cloudy days the river will come alive.  At times you will see large pods of fish working along slower banks and eddies. The Rainbows and Whitefish tend to pod up during the hatch.  Often you will go down a section of river with no activity only to round the next bend and see hundreds of fish rising. The Browns, especially the larger ones, tend to be loners, so pay extra attention to any solitary rises that you spot.

While you want to carry some specific Beatis patterns, you can often get away with a mayfly attractor like a Parachute Adams or Purple Haze. The spring Baetis are usually a bit larger than those in the fall, so #16 and #18 flies are your choices. I like to fish 2 dries at once and will typically have a larger, easier to see pattern up front, trailed by a smaller, more natural pattern as the dropper.  Another productive strategy is to fish a Beatis emerger behind your dry fly. You can load up your emerger pattern with floatant and fish it on the surface like a dry, or allow it to sink a few inches under the water and have your dry act as a strike indicator.  Sometimes fish will key in on a specific stage of the hatch, so you want to be prepared with everything from nymphs to duns.  You will still be doing a good bit of nymph fishing on sunny days, but there will be rising fish each afternoon. Cloudy days should see a window of several hours with a consistent dry fly bite.
Cloudy days will see the heaviest hatches of March Brown's and BWO's
March Browns
The March Brown is the first “big” bug to hatch each season, as these mayflies typically come in around a #12. Despite the name, March Browns hatch on the Yellowstone during the 2nd half of April into May. The March Brown hatch is typically harder to predict than the Baetis or Caddis. You won’t often find a blanket hatch of the March Browns, but they will be plentiful in scattered pockets throughout the river. These mayflies overlap both the Baetis and Caddis hatches, and you will often see them hatching at the same time on any given day. The March Browns are particularly interesting because while they are often comparatively sparse in numbers, the fish will get keyed in on them, oftentimes to the exclusion of eating other bugs. I remember witnessing this phenomenon several years ago in May during the Mother's Day Caddis hatch. We were floating below Carter's Bridge, and had dropped anchor in a run along the bank with a small back eddy where we spotted several good sized trout feeding on the surface. The trout did not respond to our Caddis patterns, so we quit casting for a moment to observe. Despite the constant stream of caddis floating down the river, the fish were only eating the occasional March Brown dun that washed by. We did not witness a single dun go by without being gobbled up by a trout.  Quickly changing flies, we were able to take several fish out of the hole before they wised up. Every now and again, on a dark, drizzly afternoon in late April or early May, you will witness a full scale explosion of the March Browns and it is quite a sight to behold. Fish often take these large mayflies with abandon, creating large splashes with each rise.

To match this hatch, I prefer a specific imitation rather than a general attractor.  While a Parachute Adams or the like will probably do in a pinch, I like to stock up on some March Brown patterns from the local fly shop each spring.  It’s one of those hatches that you are only going to see for a short window each year, but it can be spectacular, so you want to have your flies dialed in.  If there are March Browns on the water, I want one on the end of my line.
Caddis Blizzard on the 'Stone
Mothers Day Caddis
This is the main event, folks. The Mothers Day Caddis is a legendary hatch, and one of my personal favorites of the entire year. There can be a literal blizzard of caddis in the air, appearing as huge oscillating waves over the water.  The tough part is timing this hatch.  The big blitz of bugs usually lasts for a at least a week or so, but sometimes cold weather causes it to sputter or stop and start again. Water clarity is the real issue, as this hatch is jammed right up against the start of runoff. Some years everything works out perfectly, some years the entire thing gets washed away. The good news is that we can also chase this hatch on the Madison River, which remains clear due to the dams along its course. We have so much good fishing around the Bozeman area that we do not have to put all our eggs in one basket.

Back to the Yellowstone, if you and planning a trip for the hatch, look to the first week of May as your pick, but spring weather is so unpredictable that the hatch can be earlier or later. In my experience, it seems that when the water temperatures  start to creep above 50 degrees in the afternoon that signals that the hatch is eminent. When things really get cranking, you can have productive dry fly fishing all day long, although afternoons and evenings tend to be the most consistent times for fishing. The fish tend to be a bit less shy about feeding on the surface once the sun begins to get off the water.

For flies, I like an olive or tan color in a #14. Sometimes I drop to a #16 if the water is exceptionally clear. A traditional Elk Hair Caddis or X-Caddis works fine, but I prefer some version of a parachute caddis. The colored post on the parachute caddis makes it a bit easier to see from the boat. The trout will often key in on emergers during the Caddis hatch, especially during bright, sunny parts of the day. I will drop a caddis emerger off the back of my dry, and it typically catches at least as many fish, if not more, than the dry. Patterns like a Z-Wing emerger or CDC emerger are top choices.

This is one of those hatches that every serious fly angler should try and experience at some point in their fishing career. While it does breed its fair share of frustration at times, timing it right will produce enough fish stories to forget about all the rest.

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