Some Like it Hot!

This article first appeared in the 2022 Alberta Fishing Guide

Some Like it Hot!

After a long stretch of winter’s bitter cold everyone welcomes the warm breath of change come spring. No one appreciates this more than fishers who anxiously await warmer temps to bring fish and their aquatic diet to life. Although, with what feels like increasing frequency, summer brings intense and prolonged heat that makes our rivers and streams more challenging. Fishing during hot-spells requires a nuanced approach, both to land fish and to ensure the quarry has a good chance of survival if returned to the dark. 

We’ll explore how to develop your own strategy for fishing in the heat on moving water, including changes in gear setup and those sweet spots where fish are more likely to feed. Fish are more vulnerable during hot-spells so we’ll cover how to refine your sport after the take and then releasing with minimal affect. There can be one or two side-benefits during sweltering heat so we’ll touch on those too! The main purpose is to provide insight as well as hope should the summer turn into another boiler!

How Hot is too Hot?

Rising spring temperatures are the life blood to aquatic invertebrates that trout favour in their diet. There’s a predictable pattern of insect growth in moving waters across Alberta that directly effects the diet of fish.  Rising water temps through spring into summer generally encourages hatch events and the eager response of hungry trout. Even so, what happens when the daily air temps take a dramatic spike up with protracted stretches in the 30s? In short, this has a knock-on effect that raises water temperatures and influences the feeding pattern of fish and the areas where they prefer to hold.

Different trout species have slightly varying tolerances to rising water temperatures and the associated stress caused by the depletion of dissolved oxygen. When water becomes too warm fish die off. The lethal tolerance for westslope cutthroat is at the lower end near 22C, rainbows 24C, with browns a bit higher at 25C.  Local populations may acclimate modestly but the wiggle room is low with roughly 1C of latitude.  

To be clear, the temperatures stated above are lethal levels and not the upper limit for safe angling.  The exhaustion caused by playing a fish that’s already stressed from low oxygen may well be the tipping point, even if the release is done well.  No, the safe upper limit to catch and release fish is quite a bit lower at 20C (~68F), with browns perhaps a degree or two warmer.  If you intend to keep the catch then going above 20C is an option, although releasing fish played in water >20C becomes an ethical question. 

Nothing beats a simple handheld thermometer to suss out water temps on your own.  They can be purchased at any decent fishing store and are important kit for every angler.     

Early Birds and Night Owls

Trout look for ways to reduce their energy output when oxygen levels dip as water temps sore into the high teens.  They spend less time feeding, preferring instead to hold in slower water.  However, they do still feed but are more selective in the location and timing.     

A fundamental change in strategy is to hit the river at select times of day when water temps dip and fish are most likely to feed. Water temps routinely cool toward evening and through to mid-morning making early starts and late evenings a better bet. I’ve had many excursions on the Crow casting mostly by feel in the dim-light.  I’ll generally use larger flies (8-12) in very poor light, often imitating bigger stoneflies and then hoppers later in the summer.  A big tuft of white on top helps to see the fly as the light fades.      

Bubbles

Water becomes aerated by passing over rocks and drops and this creates an important niche for oxygen sensitive fish on the prowl for food. Rather than sticking to pools and slow moving runs that worked so well in cooler weather, change your sight picture to seek out areas with turbulence and bubbles.  Water that runs through riffs, rapids, rocks and drops provides elevated levels of dissolved oxygen that fish crave. A favourite approach is to look for slight elevation changes where the water thins out and breaks over the tail-end of a gravel bar, usually with slightly deeper holding water on the bottom side. Ofttimes these unassuming linear features stretch 20m or more. Layer casts up stream step by step while moving along the break, and  let the fly bob down over the rocks into the highly oxygenated holding water below.  You may be surprised at the size of fish you will pull from these spots that most others float by. Those easy-to-see stone and mayfly patterns often work well, but you can expect a dry fly to fully submerge so be prepared for light takes.     

Shade and Structure

Also, look for areas that offer shade from direct sun.  Freestone systems like the Livingston and Oldman have rock ledges with deep undercuts that provide dark cooler water below, as well as seasonal logjams providing refuge. Spring fed systems like the Raven have penetrating undercuts and more than their share of stumps and overhangs where browns lurk beyond the sun’s reach.     

Dan worked this logjam to entice a cutthroat trout to come out from the shadows.

Use Enough Gun

Heat spells are the time to switch out your light tackle for setups with heavier tippet that allows shorter playing time. This isn’t unsporting, in fact its quite the opposite by reducing the likelihood of fish becoming overwhelmed with exhaustion from lengthy fights during low oxygen levels. This may mean putting that favourite 4 wt on the rack, and instead using a 9ft 5-6wt and sticking to 4X and heavier tippet. This will affect the size of fly that will layout nicely given the larger tippet, but the trade off is worth it. As Ruark suggests, don’t get caught under gunned, while in this case its for benefit of the trout rather than the hunter.

Mayfly tricos are an important food source that commonly hatch in the early hours and again late in the evening with trout slurping them frequently. If water temps are near the 20C threshold and you’ve switched to heavier tippet, then laying out a size 20 trico would be cumbersome at best. Instead, try a larger terrestrial that matches the tippet more closely (size 12-16) to entice a feeding trout with something they associate with warmer water (eg, foam ant, beetle or bluebottle).  Of course if temps dip down again to the 16-18C range then switch over to 6-7x tippet and present those tiny #18-22 tricos!  

Too Hot to Handle

This is also the time to use a net and avoid handling fish out of water.  A net allows the hook to be removed quickly and while the fish is partially submerged. Take pictures within the net as well and ensure it is swimming on its own when liberated. With practice the entire release is quickly done. If you have a hook set deep inside the mouth then simply nip the line and let the fish go. Learn from my mistakes and avoid digging around in the mouth which can easily cause bleeding to occur.   

Cutthroat going right back to the water.

Side-Benefits

There are at least two side-benefits that come from heat spells.  If the heat arrives earlier than normal like it did in mid-June in 2021, you can expect a welcome and steady wave of hatches that may well occur a week earlier than normal. The trick is adjusting your own approach to take advantage of the situation. Which brings us to the second point - timing.  Most anglers use the day shift from 10am to 4pm which means you’re far more likely to be on your own if you switch things up. Try napping in the heat of the day while others are foaming the water with repeated casts. And, like that big brown, become more active when the sun is beyond the horizon.

Fishing during heat waves takes a nuanced approach, but you can have rewarding days if you’re willing to adjust things up. Good luck out there!