April is the only month on this site's hatch charts where Blue-Winged Olives are marked at peak on 88 of the 92 rivers. That single row makes it the most predictable dry-fly month of the year on Western trout water, and the rest of the April picture is about what else is peaking alongside the Baetis on each kind of river. This is a month page, not a season page; the broader pre-runoff picture is on the spring guide.
Blue-Winged Olives: peak on nearly every river
The Baetis peak runs across every water type in April. On the freestones it is the last big hatch before runoff: the Madison, Yellowstone, Big Hole, Bitterroot, South Fork of the Snake, Roaring Fork, Logan, and Pecos all show peak. On the tailwaters it is one more good month in a long run: the Bighorn, Missouri, South Platte, Green, and San Juan show peak. The four rivers where the row is not at peak are the three Yellowstone-area rivers whose charts are blank until May and the Lake Fork and Uinta, high Uinta Mountain freestones where it reads on rather than peak.
Carry RS2s and Baetis nymphs in 18 to 22, CDC emergers, and Parachute Adams or Comparaduns in 18 to 20. Overcast afternoons are best. See the Blue-Winged Olive guide.
Where midges are still at peak in April
Midges are marked at peak in April on 53 rivers, and the split tells you something: they have dropped to on for most of the Montana, Idaho, and Wyoming freestones but stay at peak on the tailwaters and the low-elevation water. The Bighorn, Missouri, Frying Pan, Blue, Taylor, Gunnison, South Platte, San Juan, and Lees Ferry all show peak, as do the Truckee, Owens, and Upper Sacramento. On those rivers a Zebra Midge size 20 to 22 below a Baetis nymph is still the standard April rig.
April caddis: the low rivers and the tailwaters
Caddis reach peak in April on 33 rivers, and again it is the lower, warmer water. Northern California and the coastal Northwest lead: the American, Sacramento, Hat Creek, Pit, McKenzie, Rogue, North Umpqua, Sandy, Skykomish, and Yakima. So do the Nevada and Southwest rivers: both Truckees, the Walker, Carson, East Walker, Rio Grande, Cimarron, Salt, Verde, and Oak Creek. Among the Rocky Mountain tailwaters the Bighorn, Missouri, Blue, Frying Pan, South Platte, Colorado, Shoshone, and Green River, Wyoming show April caddis at peak. Size 14 to 16 Elk Hair Caddis and X-Caddis, with a soft hackle or Sparkle Pupa swung through the riffles in the evening.
Mother's Day Caddis, Red Quill, and the first stonefly signals
A few rows are specific enough to plan a trip around.
- The Provo River below Jordanelle is the only river on the site where the Mother's Day Caddis (Brachycentrus) is marked at peak in April. It reads on in March and peak in April and May. The Middle Provo, Weber, Ogden, and Boise show it on in April ahead of a May peak.
- The Frying Pan is the only river with a Red Quill row, and it hits peak in April. Size 14 to 16 red-brown mayfly, afternoons.
- Salmonflies are marked on in April, the earliest on the site, on the Logan and the Deschutes. That is the nymph migration, not the hatch. Fish a rubber-leg stone tight to the bank on both.
- General caddis reads on in April, ahead of a May or June peak, on most Montana and Idaho freestones. First caddis of the year but not yet the blanket hatch.
The rivers with nothing on the chart in April
The Firehole, Gibbon, and Lamar show every row off through April, with the first activity in May. They are inside Yellowstone National Park and their season is set by the park, so check the park's fishing regulations rather than assuming. The high Uinta freestones in Utah, the Lake Fork and Uinta, are still mostly under snow with midges on and little else.
April at a glance by water type
| River | Water type | Marked peak in April |
|---|---|---|
| Missouri, MT | Tailwater | BWO, midge, caddis, scud/sowbug |
| Frying Pan, CO | Tailwater | BWO, midge, caddis, Red Quill |
| Provo, UT | Tailwater | BWO, Mother's Day Caddis |
| Madison, MT | Freestone | BWO |
| Roaring Fork, CO | Freestone | BWO, midge |
| Logan, UT | Freestone | BWO (Salmonfly on) |
| Silver Creek, ID | Spring creek | BWO, midge |
| Yakima, WA | Freestone | BWO, midge, caddis |
| Salt, AZ | Tailwater | BWO, midge, caddis |
An April fly box
- Baetis: RS2 18 to 22, Pheasant Tail 18, CDC emerger 18 to 20, Parachute Adams 18 to 20.
- Midge: Zebra Midge 20 to 22, Griffith's Gnat 18 to 20.
- Caddis, for the low rivers and tailwaters: Elk Hair Caddis 14 to 16, Sparkle Pupa 14 to 16, soft hackle 14.
- Stonefly nymph, for the freestones: rubber-leg stone 6 to 10.
- Check the state agency for the water you are fishing; several states have April closures on spawning tributaries.