Boulder River Fly Fishing in May

Fly Fishing Montana on the Boulder River in May

Runoff season begins in earnest sometime in early May or late April on the Boulder River. Although water clarity typically remains favorable, raging flows make fishing difficult and even dangerous at times.

Expect daily flow fluctuations early on in the runoff as river levels rise and fall along with the daily temperatures in the headwaters. As with many Montana Rivers, trout fishing is generally slow as water levels rise – even during mid-summer following a heavy rainstorm. Sparring the occasional, significant cold front which quickly pauses the runoff on the Boulder River, Montana fly fishing efforts are best directed elsewhere in May.

Boulder River Fly Fishing Hatches in May

March Brown, Green Drake, and BWO mayfly hatches can be encountered during May. Thick hatches of Mother’s Day Caddis are typically present during the early stages of the Boulder River runoff. Expect surging river flows and difficult fishing conditions, despite an abundance of insect activity.

Boulder River Fly Fishing Techniques in May

Rising river levels will create difficult and dangerous conditions for both floating and wade fishing. Nymph fishing with heavy stonefly and San Juan Worm combinations along deep pockets, next to the bank can produce plenty of trout in these conditions. However, access to the river is very limited during high water and dangerous in the spots where is permissible.

Bozeman Fly Fishing Guides Pro Tip:

Watch for rapid and sudden drops in streamflow for productive Boulder River fly fishing in May following significant cold fronts. As flows drop and stabilize, nymph fishing with stonefly nymphs next to the banks and deep pockets can be terrific. Wait for dropping flows between 700 and 1200 CFS, floating anglers should be prepared for dangerous obstructions in the river following any high water flows.

Boulder River Fly Box in May