April Fishing on the Yellowstone River

April weather, stream flows, and summary

April on Montana’s Yellowstone River from Gardiner downstream to Columbus can check nearly all the boxes for most fly fishers…if the weather Gods play fair. If heavy spring rains or an early start to summer-like temperatures occur, the river can become muddy and unfishable. Such is the nature of Montana’s longest and largest free-flowing, un-dammed freestone trout river.

Weather in April can be a variety of snow showers, sunshine, and rain showers—and all can occur on the same day. Wind, as Montana changes from winter to spring, is common on the Yellowstone River in April. But with over a hundred miles of river to fish, finding a calm section is often attainable. Armed with quality gear to protect from the weather, anglers fishing the Yellowstone in April could experience some of the best fishing of the year.

Early to mid-April is the most consistent fishing window of the month. Unless a large rainstorm moves through, flows remain stable and clear. But as the days of the month tick away, warmer weather means warmer water temperatures which means more actively feeding fish. However, warmer air temperatures can also mean spring snowmelt runoff can commence.

The ideal scenarios to maintain consistently good fishing on the Yellowstone in the second half of April are daytime highs not above seventy degrees and nighttime lows not above freezing. If this weather pattern holds for several days, anglers can experience some exceptional fishing opportunities, including the start of the famous Mother’s Day caddis hatch—which if conditions dictate, can occur in April and not May.

Fishing: What to Expect in April

On most days fly fishing the Yellowstone in April, anglers can find fish using two-fly nymph rigs. Choose beadhead or weighted nymphs that imitate mayflies, caddis, or stoneflies. Anglers willing to drag a large, heavily weighted streamer or Wooly Bugger pattern may entice one of the river’s large brown trout to strike. Dry fly anglers can find some success prospecting with attractor patterns in sizes 8-16, but, unless mayflies or caddis are hatching in abundance, many trout in the Yellowstone River prefer to feed subsurface. Because of this, dry fly-dropper nymph rigs are the go-to choice of rig for dry fly fishing on the Yellowstone in April.

If hatches of Blue Winged Olives (BWOs), March Browns, or caddis are to occur, they will emerge around mid-day. When this occurs dry fly anglers can experience a special sight—thousands of insects bundled together creating a floating mat of trout food. Depending on the type of insect species hatching, a size 16 parachute mayfly pattern or a size 14 caddis dry fly should be fished.

Experiencing a hatch of this abundance is not always a daily occurrence, but always be prepared. Due to the ever-changing weather of the month, fishing the Yellowstone River in April is multi-faceted. This day-to-day nature of the fishing action is one of the appeals of the wild and free-flowing Yellowstone—you just never know what you’re going to get.

Where to find April trout on the Yellowstone

Because water temperatures are still cold—rarely rising above 52 degrees before runoff commences—trout will be found in slower currents. Focus on the rivers slower and deeper waters—places like inside bends, eddy-lines and foam seams around large rocks or other structure. These “softer” waters allow for trout to expend very little energy while having access to available food. Rainbow trout and some rainbow-Yellowstone cutthroat trout hybrids may still be spawning on the Yellowstone, so avoid targeting spawning trout or disrupting their spawning areas.

Important April hatches

Hatches of BWOs, March Browns, and early season stoneflies are the most prevalent and consistent. The Mother’s Day caddis often starts to appear at the very end of the month. BWOs can hatch on sunny and cloudy days, but a cloudy, slightly rainy day can create a large emergence. March browns are not as prolific as BW0s, but the larger size 10-12 mayfly can entice bigger trout to the surface even during a sporadic hatch. Like BWOs, March browns will hatch in greater abundance with overcast skies. As the month progresses and local weather becomes more spring-like than winter-like, caddis can hatch in prolific numbers. Most caddis will be size 14 and 16 and are dark bodied. However, as the warmer weather ensues and month’s end nears, the risk of off-colored water and rising flows increases, thus decreasing the clarity of the water and onset of spring runoff. 

Yellowstone River fly box for April

BWO dry flies size 16
BWO emergers size 16
BWO nymphs size 16
March brown dry flies size 16
Dark bodied caddis dry flies size 14 and 16
Caddis pupae size 14 and 16
Skwala dry flies (dark olive stonefly) size 10 and 12
Stonefly nymphs in brown and black sizes 10, 8 and 6
Sculpin and streamer patterns—white and black—sizes 6, 4 and 2
Egg patterns size 12
Brown and yellow woolly buggers sizes 6, 4 and 2