Late Summer Fly Fishing Tactics

Late summer fly fishing on Colorado’s Western Slope of the Rockies can mean low water, warm water, and at times, finicky trout. Some anglers decide to hang it up and prepare for the temps to cool and the fall streamer bite to turn on. But don’t let this stop you, late summer can be some of the most enjoyable fly fishing of the year with the peak of the terrestrial season, wet wading, and who doesn’t like soaking up those sun rays of the “dog days” of summer? Below is a guide outlining how to have a productive day on the water in the late summer. The blog also covers the ethics surrounding warm water temperatures and when and where to target fish in the late summer. 

The Importance of Water Temperatures in the Summer:

Water temperatures dictate just about everything when it comes to late summer trout fishing. Warm water temperatures mean low oxygen levels for trout. With low oxygen levels, the fish cannot expand energy, and typically will not actively eat on the surface. If caught, the fish may be depleted of oxygen, and the fight can result in death. It is essential to understand water temperatures and how they pertain to ethically fly fishing for trout. Be sure to check out this previous blog on Catch and Release Tips for Late Summer Trout.

The Temperature Rule for Trout Fishing:

As a rule of thumb, water temps below 65 degrees Fahrenheit means the trout are happy and actively feeding. When water temperatures go above 65 degrees Fahrenheit, anglers need to use immediate caution. Fish need to be played faster to decrease the chance of over-exhaustion and remember to #keepfishwet at all times. When water temperatures hit 67 degrees Fahrenheit or higher, it is time to stop fishing and give the fish a break. So how do you check and understand the water temperatures?

Ways to Check Water Temperatures:

  • Temp the Water: This is the easiest way to see real live data of the water temperatures of where you are fishing. To take the water temperature, you will need to purchase a streamside river thermometer like the Fishpond Current Thermometer $18.95 or the Umpqua Stream Thermometer $12.95. Simply, take your thermometer out of your bag and let is calibrate for a minute or so. Next, dunk the thermometer for one minute in the river current (not in the backwater). Then you should have an accurate water temperature. 
  • Check Online USGS Live Data: The guides at Vail Valley Anglers utilize the live “real time” data that the USGS provides online about the different watersheds. Simply go to the USGS Current Conditions for Colorado Streamflow Website. Find the watershed that you are planning to fish. Next, click on this specific gauge of the river. For this example use the Eagle River Below Wolcott Gauge. Once on this page, make sure to check the Temperature Box and then set your date range, click go. And boom…you should see a graph of the recent water temperatures for this area. Do note that not all gauges on the USGS webpage check water temperature. You can also check the fishing reports on as there is a box that shows the temperature. You can see the Eagle River fishing report here.
  • Call or Stop by Your Local Fly Shop: Local fly shops are a great resource for anglers to figure out precisely what is going on in the local rivers and if the temperatures are getting too hot to fish. So swing by or call a fly shop that is near your intended fishing destination to get a good idea of the fishing conditions and water temperatures.
  • Check Fishing Regulations: At times, managing agencies step in and impose new regulations to protect fish due to high water temperatures. In the late summer, it is very common for fishery managers to impose a “hoot owl” rule where you cannot fish in the afternoons due to high water temperatures. So be sure to check the fishing regulations before going out fishing in the late summer. 

When to Fish: [Early bird gets the worm]

Due to the high water temperatures in the late summer, early mornings and late evenings are the best times of day to target trout. In the summer, the sunrise is anywhere from 5:00-5:30 am. Allowing anglers ample time to fish in the morning before that sun gets high and warms the water temperatures up. Once that sun gets up the water temps will rise, and the fish will become less active. At the end of the day, when that sun drops, the fish will begin to become active again, and anglers can enjoy the hour of power in the last hour of daylight.

Riffle and pocket water offer good summer fishing.

Where to Fish: [Oxygen is King]

Since there is less oxygen in the rivers in the late summer, the fish tend to congregate in the higher oxygenated areas like the riffles and upper ends of deeper pools where more water is moving through. Where there is current, there is oxygen. It can be a great time of year to work more technical pocket water with a dry dropper set up. Or work a nymphing rig through a fast riffle. 

Another area to fish this time of year is the higher elevation creeks and streams. These higher elevation systems will typically have cooler water temperatures and happy fish. So get out the topo map, find some blue lines, and head out to explore. 

Dam controlled tailwaters can also provide ample fishing opportunities if the flows are still up. On the Colorado River in the late summer tributaries like the Blue River can provide an increase in water flows. This increase in flow will provide the Colorado River with cold oxygenated water. It is important to check the flows of the specific river systems you plan to fish and see if the flows are average for that year or not. When the flows are below the annual average, it is a red flag that the water temperatures will be high. 

VVA Guide Justin Carr rigging up for a summer float.

Fly Selection: [Terrestrials and midges of my!]

In the late summer, there are drastic changes in water temperatures within a fishing day, so it is crucial to understand the different flies needed to be successful. 

Early mornings: This is your best chance to fish dry flies. The water temps are cool enough to entice a smart fish to come up and slurp a well imitated dry fly. It is also most likely the first fly that this fish will see of the day. Try just throwing a single dry this time of day. Mayfly and midge patterns seem to be most effective this time of day. 

Effective dry fly patterns include, Parawulff #16-20, Patriot #14-#18, Renegade #18-20, Sprout Midge (black) #18-22, Griffiths Gnat #18-22, and Extended Body PMD #16-18.

Late morning: Once the sun gets higher, it begins to wake those bugs up, and the fish start to key in on hatches. Dry flies can still be the ticket, but try adding on a dropper to entice a below surface eat. 

Recommended patterns: Royal Stimulator #14-18, Hackle Stacker #16-18, Chubby Chernobyl #8-14, Amys Ant #12-16, Frenchie #14-18, Perdigon #14-18, Soft Hackle Phesant Tail #14-18, Guides Choice #14-18.  

Middle of the day: The sun is high, and the water temperatures are on the rise. The bite will be mostly subsurface as the fish will become lazier with the warmer water temps. Nymphs are most effective except for some sporadic terrestrial eats like ants or hoppers. 

Recommended patterns: Chubby Chernobyl #8-14, Swisher Foam PMX (Black, Grey, Tan) #8-12, Swisher PMX (Royal or Yellow) #6-14, Black Foam Ant #10-14, Posion Tung #18-22, Magic Fly BWO/PMD #18-20, RS2 #18-22, Rainbow Warrior #18-22, and Zebra Midge #18-22.

Evening bite: As the sun begins to set, the fish start to move out of the faster water to search out food, and it is a good time of day to get a fish to come up to the surface or have a fish eat a streamer imitation.

Recommended patterns: Elk Hair Caddis #14-18, Stimulator #14-16, Chubby Chernobyl #8-14, Green Drake Hairwing #12-16, Royal Wulff #12-16, Thin Mint, Baby Gonga, and Sparkle Minnow. 

Fishing Techniques for Late Summer: 

The fluctuating temperatures within a day make late summer fly fishing techniques vary based on the time of day you are fishing. In the early mornings, standard dry fly fishing is the most effective. As the sun rises and the water temps begin to warm, add on a dropper to your dry fly setup. Once the sun is high and heat is prevalent, switch to nymphing deeper riffles. Smaller midge patterns are the most effective during these warmer days, although there can be some mayfly hatches throughout the day. When these mayfly hatches occur like a PMD hatch, the trout will key in on this and will go on a feeding frenzy trying to capitalize on this bug hatch.

If you want to stick out the dry fly bite, terrestrials are the preferred pattern in the middle of the day. Grasshoppers and ants are typical bugs to try to imitate. On the windier days, the gusts of wind will blow in terrestrials from the banks and will create a hatch. As the sun sets, dry flies become the technique of choice, and fish will typically come up to a well-presented caddis imitation. 


Late summer fly fishing can provide anglers with many challenges from low flows, fluctuating water temperatures, and lazy fish but, by correctly understanding the basics of what to expect, you can have a successful outing. Whether it’s the 5 mile hike you took to get to a gem of a small creek, the 40 foot dry fly cast, or the hopper fly that got smashed under the tree, late summer can be some of the most memorable fly fishing memories of the year. So get out there and remember to #keepfishwet! 

Be sure to check out our up to date fly fishing reports here and our summer guided trip options

Patrick Perry, Content Contributor, and Former Guide, @patperry