April Fishing on the Ruby River

April weather, stream flows, and summary

The Ruby River in April is a mix of two very distinct fisheries—the river below Ruby Dam and the river upstream of Ruby Reservoir. Beginning around 6,500 feet in elevation in the Gravelly Range near the Montana-Idaho border, the Ruby River flows for nearly 80 miles to join the Beaverhead River near Twin Bridges. As the river flows out of Ruby Dam at an elevation of 5,000 feet, April fly fishing on the Ruby River can be consistently good if conditions allow. Because the Ruby River spans a wide range of elevation, the river above Ruby Reservoir in April is often still in winter mode, so the river below the reservoir should be the main focus of anglers. 

Above the reservoir, stream flows average between 100 and 200 cubic feet per second (cfs). Below Ruby Dam, stream flows fluctuate a little wider—around 50 cfs early in the month and around 150 cfs toward the end of the month. Despite the increase in stream flows as the month progresses, the fishing on the Ruby River above- and below-the reservoir remains consistent. 

April on the Ruby River is considered one of the wettest months, however the average monthly precipitation is only slightly above 1.5” of rain and ¾ inch” of snow. In the beginning of the month both sections have clear water. However, as the weather warms towards the end of April, the river upstream of the reservoir can begin to rise and clarity decreases, making fishing more challenging.  

As the end of the month nears and air temperatures can rise above 75 degrees F, snowmelt runoff can commence on the river above the reservoir. Since conditions—and stream flows below Ruby Dam—can change daily, it is best to check locally before committing to fish a specific section. 

Fly fishing the Ruby River in April is a mix of variable spring-like weather paired with consistently good fishing. Hatches of Blue Winged Olives dominate the hatch charts throughout the month with a few sporadic midges. Above the reservoir in April anglers are sure to find aggressive fish, while downstream of Ruby Dam brown trout dominate. 

April fishing: what to expect

A day fly fishing the Ruby River in April above the reservoir is going to be less reliable than a day below Ruby Dam. For that reason, it is best to focus on the river downstream of Ruby Dam.

Because water temperatures rise throughout the month, the length of time during a day that trout actively seek out food increases in length. During April hatches become more consistent and trout feed more regularly. Blue Winged Olive (BWOs) mayflies provide the bulk of the hatch activity, followed by sporadic hatches of midges. 

Tandem nymph rigs dead-drifted in some of the deeper runs will catch the most fish on the Ruby River in April. BWO nymphs in size 16 and 18 are the most proven patterns along with various midge patterns in size 18 and 20. Because the water below Ruby Dam can be clear, most anglers use 4X and 5X fluorocarbon tippet with nothing shorter than 9-foot leaders. 

For anglers desiring to target some of the Ruby River’s more aggressive brown trout, streamer fishing on the Ruby River in April can also be successful. Floating lines are satisfactory and dead-drifting or stripping streamers often entice predatory brown trout. 

The challenge in fly fishing the Ruby River lies in being able to cover enough water to appropriately fish for the river’s wild trout. If stream flows are above 100 cubic feet per second (cfs) walking-and-wading anglers may struggle to walk-and-wade without trespassing onto private property. Ample public access sites exist in the first six miles of river below Ruby Dam, however over-zealous private landowners own property surrounding each of the small plots of public access limiting anglers' free range.

Where to find April trout on the Ruby

As water temperatures warm in April and hatches of Blue Winged Olive (BWOs) increase, trout become more active and feed more consistently. Keep mind, however, that water temperatures are still cold—rarely rising above 52 degrees. This cold water is especially true above the reservoir. 

On the river below Ruby Dam, focus on the river's 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. 

Above the reservoir, in early April focus on deep holes and the slow water of inside bends. As the month progresses, and if fishing is still an option if flows have not risen too high—usually above 200 cubic feet per second (cfs)—trout may move to feeding lies if a hatch of BWOs happens. 

If hatch a occurs, look for trout to move into feeding lies. In April, hatches of BWOs will most likely make up the bulk of the hatches. Target slower water near bankside structure or the tailouts of longer, slower runs. 

Rainbow trout and some rainbow-Westslope cutthroat trout hybrids may still be spawning on the Ruby River in April, so avoid targeting spawning trout or disrupting their spawning areas.

For fishing streamers on the river downstream of Ruby Dam, target the typical brown trout hangouts. These are places where an aggressive brown trout can wait and then ambush prey. These include drop-offs downstream of riffles, undercut banks, overhanging or submerged structures, or structures along the bottom in a deep hole. 

Important April hatches

April hatches on the Ruby River are entirely dependent water temperatures—both above the reservoir and below the reservoir. If they are sustained in the high 40 degrees F, hatches of Blue Winged Olives (BWOs) can be a daily occurrence. On sunny days these mayfly species will trickle off and may not bring trout to the surface. On cloudy days expect more intense hatches and look for rising trout in slower water.  

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

Although not a hatch in the proverbial way anglers think of hatches, scuds and sowbugs make-up a moderate percentage of a trout’s diet on the Ruby River below Ruby Dam. Oftentimes thought of as the same insects, a scud resembles a freshwater shrimp and a sow bug looks like a “rollie-pollie” bug. These are fished subsurface, near the bottom where scuds and sowbugs reside.  

Ruby River fly box for April

BWO dry flies size 14 to 18

BWO emergers size 16

BWO nymphs size 16

Scuds and sowbugs in sizes 14 and 16

Midges, pupae, larvae, and dries in size 18 and 22

Crayfish patterns in sizes 2 to 8

Sculpin patterns in sizes 2 to 6

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