April Fishing on the Smith River

April weather, streamflows, and summary

Montana’s Smith River flows for over 60 miles through the heart of Montana. Beginning in the high ranch country of the Castle and Belt Mountains then flowing through a majestic limestone canyon, the Smith River is a wild trout river truly in a class all its own. Carefully managed by the state of Montana to protect and enhance the fishery and the river corridor, a fly fishing trip on Montana’s Smith River is not to be missed. 

Because nearly all fishing trips on the Smith River require multiple overnight stays—the main access points are 60 miles apart and anglers must apply for a permit to float and camp on the river—a fly fishing trip in April requires careful planning and a thorough understanding of river conditions and weather patterns. 

The Smith River is the only river in Montana that requires a permit for all outfitted guests and private users. There are only a few outfitters that are permitted to operate on the Smith River. Private users can apply for launch via a lottery system operated by Montana Fish, Wildlife and Parks. For launches in April, anglers must apply in February. Information can be found online at Montana’s Smith River State Park.   

Weather on the Smith River in April covers a broad range of conditions. Early in April the average daily high temperature rarely tops 50 degrees F, but by the end of the month the average daily high temperature rises to almost 60 degrees F. April receives an average of 1 inches of measurable precipitation, with half of that falling as snow and half falling as rain. 

Streamflows in April can be relatively unpredictable due to the possibility of changing weather conditions. Early in April if cold weather persists mountain snowpack may still be frozen therefore flows will be too low to float. In most years, from mid-April on, enough snowpack is melting, creating favorable floating conditions. 

April fishing: what to expect

Because the Smith River is primarily a river fished from boats, knowledge of streamflows and river-camping is crucial. On any given day in April, streamflows will rarely top 800 cubic feet per second (cfs), yet in early April streamflows can be too low to float. For most experienced Smith River anglers, flows below 150 cfs mean large rafts will drag bottom in certain sections of the river. At flows above 150 cfs and up to 800 cfs, rafts navigate the Smith River with ease. Above 800 cfs it is strongly advised to have some rafting and rowing experience. 

Most anglers spend no less than three and not more than five nights on the river. To ensure safety and enjoyment, proper planning is crucial. This includes the following: having the necessary gear, knowing how to prep and prepare meals, some rowing experience, and a knowledge of individual group dynamics. It can’t be stated enough that these things are crucial to getting the most out of a Smith River fly fishing trip.

After knowledge of weather and pre-trip planning is gained, the fishing in April is often quite consistent. Skwala stoneflies can provide the first dry fly fishing on the season and Blue Winged Olive (BWOs) mayflies can be thick on cool, overcast days, which are quite common on the Smith River in April. Because brown trout predominate in the Smith River, streamer anglers in April can enjoy some solid action for trout up to 23-inches, with trout from 14 to 16 inches being the most common. 

The Smith River is home to healthy populations of stoneflies, caddis, and mayflies. In April stonefly nymphs are very active and it is a good idea to fish a stonefly nymph as part of a two-fly weighted subsurface nymph rig or as the dropper on a dry fly-dropper nymph rig. Choose stonefly nymphs in sizes 8 or 10 and mayfly or caddis nymphs in sizes 10 to 16. 

Streamer anglers should choose streamers in sizes 4 to 8 and in olive, black, brown, or black-olive combinations. Casting to structure and stripping back to the boat or casting behind the boat and letting the fly drift past structure are time-tested methods to entice a predatory brown trout into striking at a streamer. 

Where to find April trout on the Smith River

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. 

A defining characteristic of the Smith River are its towering limestone cliffs. As the river meanders through the canyon, its currents run into, against, and along the cliffs. This is an ideal habitat for trout providing current for food and cover from predators, these canyon walls create holding and feeding lies galore. Large brown trout can be caught fishing the currents along these canyon walls and they should be fished, but in April many of the Smith River’s trout prefer the slower water downstream of a canyon wall or the soft inside bend across the river from the faster current along the wall. 

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. If caddis hatch, fish may move to faster water, but because the water temperatures are still cold, expect to find fish in slower water. 

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

Important April hatches

Hatches of Blue Winged Olive (BWOs) mayflies, Skwala stoneflies, and March Browns are the most prevalent and consistent. Skwala stoneflies are sporadic but a well presented skwala pattern in size 8 or 10 can entice a fish to rise. 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.  

Smith River fly box for April

Caddis pupae size 12 to 16

Caddis CDC emergers size 12 to 16

Caddis dry flies with dark grey, black or brown bodies in size 12 to 16; 

BWO dry flies size 14 to 18

BWO emergers size 16

BWO nymphs size 16

March Brown dry flies size 14 to 16

Skwala stonefly dry flies in size 8 and 10

Stonefly nymphs in brown and black in sizes 10, 8 and 6

Sculpin patterns in sizes 2 to 6

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