May Fishing on the Madison River

May weather, stream flows, and summary

Similar to April, May is a month of transition on the Madison River. Anglers desiring a variety of fishing opportunities will relish in the unique nature of fly fishing the Madison River in May. As the region ultimately leaves winter in the rearview, fishing in early May is often drastically different than fishing later in the month. This is due entirely to the range of weather occurring throughout the month. 

The average daily high temperature in May is just over ten degrees F warmer than April. Because of this increase in air temperature, water temperatures follow suit and are favorable for active trout. Most rainbow trout finish spawning, hatches of caddis are common—especially on the Lower Madison River near Bozeman. Anglers worry less about enduring the cold, but need to factor in the possibility of impending snowmelt runoff

May on the Madison River is considered one of the wettest months, however the average monthly precipitation is only slightly above 2” of rain and 1” of snow. This small amount of precipitation paired with the fact the river has two dams, means there is rarely a day in May on which the Madison River is too off-color or muddy to fish. Even on these days—when snowmelt runoff creates dirty water—the Madison’s trout continue to feed. 

As the end of the month nears and air temperatures can rise above 75 degrees F, snowmelt runoff can commence. When this occurs, a few smaller tributary streams can run high and muddy. Since conditions can change daily, it is best to check locally before committing to fish a specific section. 

Fly fishing the Madison River in May is a mix of pleasant summer-like weather or variable spring-like weather paired with consistently good fishing. The anticipation of the Mother’s Day caddis hatch on the river near Bozeman and the warming water temperatures on the river upstream of Ennis and towards West Yellowstone, create a month’s worth of fly fishing in which any given day can be exceptional. 

May fishing: what to expect

A typical day fly fishing the Madison in May begins with choosing which section to fish. The “upper river” above Ennis lake and the “lower river” below the lake behave differently in May. On the river upstream of Ennis anglers should consider fishing weighted two-fly nymph rigs below a strike indicator unless there is a strong hatch. Various mayfly and stonefly nymphs dead-drifted or slowly swung will pick up most fish. On cloudy days strong emergence of Blue Winged Olives (BWOs) or March Browns will produce pods of rising trout in the slicks behind rocks or in the slower runs that are more prevalent near Ennis. 

On the lower river dry fly anglers can expect the Mother’s Day caddis hatch on the Lower Madison downstream of Ennis Lake and downstream towards Three Forks. This hatch is appropriately named because it often begins around Mother’s Day. Above Ennis Lake, if the weather is cool and rainy, hatches of BWOs can occur in abundance. March Browns hatch on the lower river and the upper river as well. The Mother’s Day caddis hatch on the Lower Madison can last into late May. For the caddis hatch, choose a dark grey or brown-bodied caddis dry fly in sizes 12 to 16. BWOs and March Browns that hatch on the Madison in May are often size 14 to 16 and 12 to 14, respectively. 

Because water temperatures rise throughout the month, the length of time during a day that trout may actively seek out food increases in length. Compared to April, hatches become more consistent and trout feed more regularly. If tributary streams—usually the West Fork on the upper river or Cherry Creek on the lower river—rise and create muddy or off-color water on the main river, the dry fly bite can wane. If this occurs, rig a larger weighted fly like a Woolly Bugger or crayfish for the first fly and then a smaller nymph for the second. Even in clear water the tactic of fishing a big-fly-and-a-little-fly can be a good way to entice some of the river’s larger fish.

Where to find May trout on the Madison

With increased hatches of caddis, BWOs, and March Browns, trout follow the food source. They begin to migrate from slower, deeper pools and can be found in a wider variety of habitats. As each day can bring unique weather, the fishing action on a day-to-day 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 BWOs target slower currents, eddy lines, and seams behind rocks. When caddis are thick, look for rising fish in riffles, bank-side structure, or foam lines created by mixing currents or structure.  For March Browns, focus on slower runs and soft water downstream of structure. 

Important May hatches

Hatches of BWOs, caddis, and March Browns occur in May. However, the Mother’s Day caddis is the primary hatch of the month. Appropriately named, this hatch mostly occurs on the Lower Madison River west of Bozeman and downstream of Ennis Lake. As the water temperatures climb to 50 degrees F, these insects can hatch on sunny or cloudy days. BWOs will hatch in abundance on cloudy, rainy days but on sunny days might only hatch in small numbers. Hatches of March Browns are sporadic in May, but when they do hatch, some of the river's largest trout prefer these larger—size 12 to 14—mayflies. 

Madison River fly box for May

BWO dry flies size 14 to 18

BWO emergers size 16

BWO nymphs size 16

March Brown dry flies size 14 to 16

Caddis pupae size 14 to 16

Caddis CDC emergers size 14 to 16

Caddis dry flies with dark grey, black or brown bodies in size 14 and 16; 

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

Skwala dry flies in peacock in sizes 10 or 12

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