Mark Melynk worked in partnership with Visit Idaho to create this Travel Tip.

Fly fishing is an incredible sport where almost everyone can participate. One of the great things about fishing on the fly is if the water isn’t ice, and regulations allow, you can target some fish species 365 days a year. There are times where you’ll definitely have to bundle up to keep warm, and times where you’ll be grateful to be waist-deep in a river cooling off.  Depending on the seasonal conditions many Idaho fish species will prove to be worthy adversaries to fly anglers no matter the season.​​​​​​​

couple fishing near Stanley
Fishing, near Stanley. Photo Credit: Idaho Tourism.

The state of Idaho is fortunate to have a great number of exceptional trout streams within its boundaries. And I truly mean exceptional! There are so many choices for anglers. Often, as fly fishers, we look for any excuse to experience anything fly fishing when we aren’t on the water, be it fly fishing films, articles, or researching new gear or locations. ​​​​​​​​​​​​​​Idaho is big and the opportunities to catch fish on the fly even bigger. Let’s look at Idaho’s seasons on the fly as a whole using one specific river system. This overview can then be transferred to any river you want to fish with a little research online and a little more once you’re there, and of course, popping into a fly shop and speaking with the locals is a great approach as well.

I love the South Fork of the Snake River in Eastern Idaho. So, we’ll base our seasonal template on that.  Here are some considerations to keep in mind when looking at where to fish in Idaho.

small insects on top of water
Photo credit: The New Fly Fisher

What Fish Eat

A trout’s food sources change all the time be it hour by hour or month by month. The offerings in and on the water are never the same. It’s a great idea to find the online hatch chart for the river you are fishing. These charts have been developed through experience by guides and recreational angling residents intimate with the river and its tributaries and reflect regular seasonal weather.  These charts indicate when certain bugs will pop and where on the river.  That information will help you in your fly selection heading out.  These hatch charts will also allow you to “cherry-pick” certain feeding events that you may want to experience like the grasshopper bite in late summer. Though every river is different, there is no mistaking the sound of a trout eating a hopper off the surface, and watching a big trout eat your foam grasshopper is for many 100% addicting! ​​​​​​​

There are, however, a few flies you should always have with you.  These represent food sources that fish will feed on opportunistically all year long but tend to fish better when there typically isn’t a hatch going off. Streamers and woolly buggers replicating baitfish and leeches or even crawfish will span the days where it may be too cold for bug activity. ​​​​​​​

smiling man in a hat casting a fishing line into the river
Get ready for an angling adventure on the Payette River. Photo credit: Idaho Tourism.

Water Temperature

Water temperature is one of the more vital factors in deciding when, where, and how to fish. A general rule for trout is the colder the water is, the slower a trout’s metabolism will be.  In the spring and fall, when water temperatures are low, you can’t beat fishing slow stripped streamers trying to get the offering right in front of the fish.  The key here is to cover the water to entice a fish to eat without expelling much energy.​​​​​​​

As the season warms up, you’ll generally see increased fish metabolism, increased bug activity, and an increased willingness for a trout to come and eat a dry fly. Water temperatures between the mid-50 degrees to about 69 degrees Fahrenheit is your prime time for insect hatches with the low 60s being the sweet spot.  If the water temperatures eclipse 70 degrees Fahrenheit, it’s a good idea to switch things up and target available warm water species. In temperatures that exceed 70 degrees Fahrenheit, oxygen levels may be lower and anglers risk causing undue stress on fish.

silhouette of man fly fishing in river
Photo credit: The New Fly Fisher.

The Spawn

Cutthroat and rainbow trout are spring spawners. Brown trout spawn in the fall.  Fishing these fish before the spawn for brown trout and after the spawn for cutthroat is often some of the most exciting fishing you can experience. 

Firstly, post-spawn cutthroat and rainbows are on the hunt for protein. They are looking to replace the weight and fat loss during the act of redd (nest) making and the physical toll spawning takes on each individual.  When they start to focus on food again, they will aggressively attack larger offerings in an effort to replenish themselves as quickly as possible.  Brown trout in the pre-spawn are territorial. They will vehemently defend the lair they have worked so hard to find and protect. They will become more and more aggressive toward intruders as they get closer to the spawn until they eventually leave. Often the worst the weather in these fall months, the better the fishing may be. 

These three seasonal considerations are but a few important factors in deciding when, where and how in Idaho you want to fish. The best bet is to reach out to a guide or outfitter and simply ask some questions. Maybe even book them for a day or two once you’ve nailed down your desires. There is a multitude of opportunities available in Idaho to explore and learn about the fish and the seasons and how they behave. Get out there, bring your sense of adventure, and fish the seasons of the fly in the great state of Idaho.​​​​​​​

Feature image credited to The New Fly Fisher.

Mark Melnyk is a host/producer/partner at The New Fly Fisher Television Show now entering its 21st year of broadcast. With a palpable love for fly fishing and adventure, you’ll often see Mark chasing fish all over North America and the Caribbean. When he’s not casting flies, he lives in Ontario, Canada, is married with two aspiring fly fishers in training.

Published on July 27, 2021