Rocky Mountain Runoff, What You Should Know

Provided by the team at Yellow Dog Flyfishing Adventures

As springtime arrives in the Western United States, trout come to life in search of food. Some of the season’s best fishing conditions can be in late spring and early summer, but with high water and runoff, anglers are faced with a unique set of challenges. With a few pointers, however, anglers can ensure runoff is productive and safe.

What is runoff?

Runoff occurs every spring in states like Montana, Colorado, Idaho, and Wyoming. As snow melts in the mountains with warm temperatures, millions of gallons of melted snow drain into high alpine streams and creeks eventually flowing all the way into river systems like the Yellowstone, Missouri, and Snake. On a large freestone river like the Yellowstone, runoff flows can be as high as 30,000 CFS. (A basketball has an approximate volume of 1 CFS – imagine 30,000 basketballs rushing by every second and you have an idea the amount of water and force.) In spite of all the water, trout remain in the river seeking protection and food during the deluge.

Where are trout during runoff?

Anglers face two challenges during runoff: muddy water and fast currents. With water visibility almost nonexistent, it’s difficult for trout to not only see a fly but feel safe enough to eat a fly in the rushing current. For these reasons, successful fly fishermen focus on accurately casting to protective structures. Trout will seek shelter from the current behind rocks and clumps of willows, insides of river bends, slow-moving or slack water along banks, eddy seems, stands of submerged cottonwood trees, the bottom-side of islands and sandbars, behind downed trees, and even in the mouths of small creeks and feeder streams. After narrowing fishing efforts to those places most-likely to hold trout, it’s important to select appropriate flies.

Fly selection during runoff.

Trout have a wide selection of food sources during runoff as earthworms, ants, beetles, and countless insects are swept into the river. A San Juan worm is generally a great fly selection that trout can easily see and are notorious for loving. When in doubt, choose a fly that most closely resembles the river’s natural food sources. Keep in mind that tailwater rivers usually have more biomass than freestones, in which case, scuds and sowbugs have been proven to be extremely effective.

Be Careful

Lastly, be careful. Use common sense and exercise caution. Not only is the river inundated with a tremendous amount of racing water, but water temperatures are regularly in the low 40’s. A misstep and swim can quickly turn lethal. While runoff presents several challenges to anglers, it is also a great chance to hook into some terrific fish – arguably some of the largest fish of the year. Good luck out there and enjoy everything that fly fishing has to offer.

Current Runoff Conditions

Snowpacks throughout the Rockies are between average and great, as most river basins are sitting just below or above-average levels for this time of year. After the typical runoff that occurs in April and May, we can start feeling good about our summer fly fishing season on the rivers and creeks of Colorado, Idaho, Montana, and Wyoming. For more information on current snowpack levels, please visit this link.

Ready to hit the water this summer? View some of Yellow Dog’s favorite Wyoming, Idaho, and Montana fly fishing trips for more information!

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