April Fishing on the BigHorn River

April weather, stream flows, and summary

The Bighorn River in April is one of the most consistent spring fisheries in all of Montana. While many rivers further west may still be in winter mode, the Bighorn River is in full-on “go” mode by April 1st. With very active midges and a strong emergence of Blue Winged Olive (BWOs) mayflies, the tailwater section of the Bighorn River east of Billings, Montana offers anglers a kick-start to their angling season. 

Fly fishing on the Bighorn River in Montana consists of the twenty-six miles of flowing water downstream of the afterbay at Yellowtail Dam. Here, clear and cold water flows from the man-made structure. This cold water provides ample habitat for hatches and trout. Only four public access points are available to anglers on the first twenty-six miles of river. And, it is here where most of the fly fishing occurs. Additionally, the river upstream of Bighorn Fishing Access Site provides the highest concentration of fish—well above 4,000 trout per mile. For good reason, most anglers only fish the river above the  Bighorn Access site. 

Weather in April is a mix of all four seasons—sunshine and bluebird days, rain and drizzly days, and a few days of snow and blizzard-like conditions. The potential exists for all of these to occur on the same day. Daily average high temperatures increase throughout the month, with early April seeing daytime highs in the mid 50 degrees F and by month’s end the mercury rising to average in the mid 60 degrees F. Less than 1.5” of measurable precipitation falls in April, with less than .02” of that falling as snow. Armed with quality gear to protect from the weather, anglers fishing the Bighorn River in April could experience some of the best fishing of the year despite variable weather conditions.

Floating is the primary method to fish the Bighorn River, as only four access sites exist. Stream flows in April historically average around 2,500 to 3,500 cubic feet per second (cfs) creating ideal conditions for float and walk-and-wade fishing. Many walk-and-wade anglers utilize the access sites and then walk upstream or downstream. The Bighorn River’s small sized cobble bottom is easily waded. Floating anglers also primarily use the boat to float from one area to the next, parking the boat and hopping out to walk-and-wade a productive riffle, run, or flat.  

April fishing: what to expect

Because the Bighorn River lies in eastern Montana and at elevations below 3,200 feet, April on the Bighorn River fishes more consistent than other rivers in Montana. In most years stream flows allow for exceptional walk-and-wade fishing, however it is best to have a boat to access to the best runs, riffles, and flats. 

Anglers on the Bighorn River in April can expect strong hatches of Blue Winged Olive (BWOs) mayflies and consistent action with midges. A typical day fishing the Bighorn River in April often begins fishing a two-fly weighted nymph rig with size 16 to 20 midge or mayfly nymphs, then around mid-day the BWOs begin to hatch and anglers with moderate casting ability switch to targeting trout eating BWOs on the surface. 

For tandem nymph rigs most Bighorn River anglers use 9- to 12-foot leaders with 4X and 5X fluorocarbon tippets. Dry fly anglers fish nothing shorter than 12-foot leaders and often use 5X and 6X, supple, monofilament tippets. Successful patterns include Wondernymphs, JuJu Baetis, Hairwing Duns, and CDC Sparkle Duns. 

Streamer anglers on the Bighorn River in April will find plenty of aggressive trout. Because brown trout are the predominant species on the Bighorn River, anglers committing to fishing streamers should find plenty of action. Slowly stripping streamers is the most common method for catching Bighorn River brown trout on large flies, but lately more and more anglers are dead-drifting or dragging streamers from a boat. Sleek, but weighted flies are the best choices in solid colors. Black and olive seem to catch the most fish, but white, yellow, and brown produce well. Generally speaking, on the Bighorn River experienced streamer anglers choose a light color on a sunny day and a dark color on an overcast day. 

The Bighorn River is also home to massive populations of scuds and sowbugs. These aquatic insects do not hatch like a midge or a BWO, but Bighorn River trout gobble up these subsurface insects on a regular basis. Dead-drifting Ray Charles, Firebead Sowbugs, Carpet Bugs, and other scuds and sowbugs in April is a great way to pad the numbers if a hatch of BWOs is non-existent or if brown trout are not chasing streamers. 

April sees some of the Bighorn River’s rainbow trout still spawning or recovering from spawning. To ensure the long-term health of the river’s rainbow trout population do not target actively spawning trout. Also do not cast on or near any redds. Additionally, if a spawning or spawned-out trout—skinny, dark in color and has the appearance of just looking beat-up and tired— is caught, please release as quickly as possible. 

Where to find April trout on the Bighorn River

If a hatch of Blue Winged Olive (BWOs) mayflies doesn’t occur, most Bighorn River trout will be in deeper, slower water because that is near the available food. In this deeper slower water, fish are probably eating midges, scuds, or sowbugs. The Bighorn River is home to thousands of fish per mile and any small change in depth or break in current can create a holding lie. If fish are not rising or actively feeding near the surface, it is highly likely they are still feeding. Target any change in current speed or change in depth, such as a bucket or small depression where the depth may be a foot or so deeper than the nearby bottom structure. 

As the month progresses and hatches of Blue Winged Olives increase trout will follow the food source. They begin to migrate from slower, deeper lies and can be found in a variety of habitats. As each day can bring unique weather, the fishing action on a day-to-day basis is unique as well. Before noon most fish will be found in slower, deeper water and then as a hatch begins the fish will adjust their locations based on the available insects. During a hatch of Blue Winged Olives target current seams, a slow seam next to a fast seam, any shallow water adjacent to any deep water, eddy lines, and seams behind rocks or seams created by faster water being slowed down by slower water. 

After a few days of warm weather and consistent hatches of Blue Winged Olives, many of the Bighorn River’s trout move to large seams and foam lines created by submerged structure, or they may lie near the drop-off of a long riffle just before the water enters a deep run. Well-presented two fly weighted nymph rigs can rack up trout numbers in these current seams. However, dry fly anglers must be patient because Bighorn River trout often require a thick hatch to surface-feed in these heavy seams.  

Important April hatches

April hatches on the Bighorn River are entirely dependent on the temperature of the water being released from the dam. Although regularly consistent from year to year, there are occasional variations. For example, in 2018 releases from the dam were well above 5,000 cubic feet per second (cfs), this resulted in very weak hatches of Blue Winged Olives (BWOs) throughout April. 

In most years water temperatures hover in the high 40 degrees F, creating strong hatches of BWOs. On sunny days this mayfly species will trickle off and may not bring trout to the surface, but Bighorn River trout are most likely chowing on them subsurface. On cloudy days expect more intense hatches and look for rising trout in slower water runs, or along seams. 

Midges are active year-round on the Bighorn River and make-up a massive chunk of a Bighorn River trout’s diet. Fishing midge patterns is best done subsurface as part of a weighted two fly rig. 

Scuds, sowbugs, aquatic worms, and craneflies are abundant in the Bighorn River, with sowbugs most likely accounting for over half or a Bighorn River trout’s diet. Strictly subsurface, these insects are active throughout April and available to hungry trout. Scuds and sowbugs are not exactly what an angler may think of when it comes to hatches. Oftentimes thought of as the same insects, a scud resembles a freshwater shrimp and a sowbug looks like a “rollie-pollie” bug. Even if they are different, a trout on the Bighorn River in April often gobbles-up a well-presented scud or sowbug. 

Bighorn River fly box for April

BWO dry flies size 14 to 18

BWO emergers size 16

BWO nymphs size 16

Scuds, especially in pink, in sizes 10 through 20

Sowbugs, especially in pink, in sizes 10 through 20

Midges in sizes 16 through 22

Sculpin patterns in sizes 2 to 6

Streamers in olive, black or brown in sizes 2 to 6