How to Fly Fish Pocket Water- Targeting Trout Around a Single Boulder
Updated: Mar 5
This article is part of a larger installment on how to fly fish pocket water. Check out Part 2 and 3 here:
How to Fly Fish Pocket Water: Rock Gardens
How to Fly Fish Pocket Water- Casting, Mending, and Line Management
Also, check out more articles from the Reading Water Series:
Improve Your Skill at Reading Water for Fly Fishing: Riffles
First, What Is Pocket Water?
My Definition of Pocket Water- Pocket water is an area where a river or stream's current is affected by objects (like boulders, logs, bridge pillars, etc.) to create fast, turbulent current as well as calmer "pockets" of water where trout prefer to position themselves in order to feed more efficiently.
What pocket water looks like varies greatly due to the depth and velocity of the river/stream, the size of the objects, the substrate of the river (sandy, pebbly, rocky, etc.), the course of the river/stream (bends or straight-aways), and so on. All of these factors culminate to make a habitat riddled with nooks and crannies where trout can hide, and to effectively fly fish just a thirty yard section may easily take an hour to fully cover it. This presents a thrilling experience of hunting and trying to catch trout in pocket water!
Pocket water is also best fished when water temperatures climb above 50°F, any colder than that and trout will typically seek out calmer, slower pieces of the river. When trout are in pocket water they can be very opportunistic feeders due to the limited time they have to snatch food as it passes by. That means matching exact insects may not be as necessary in pocket water, in fact presenting your fly to the right spot is arguably more important and will help you to hook into trout, and that's what this article is all about.
Analyzing Where Trout Position Around A Single Boulder
To begin to understand the intricacies of pocket water, it is advantageous to first look at the unique hydrology around a solitary boulder and where trout frequently station around it. We will look at a single boulder that is protruding out of the water and is not affected by current formed from any other rocks, logs, or objects (that will be covered in Part 2 of this series).
The first thing to note about finding the 'ideal' boulder is looking for one that is positioned in moderate current (i.e. about the speed of a brisk walk) since it can form great feeding and hiding spots for trout. If the boulder is in too fast of current then it becomes more of a washing machine where trout will struggle to hold their position. The opposite, current that is too slow, also is not as ideal since less food will drift downstream to the trout.
So with is in mind, take a look at figure 1 below and let's assume that this boulder is positioned in moderate current:
Trout Located in Front of A Boulder
In figure 1, the boulder has a few trout stationed around it. The first trout is located in front of the boulder (i.e. the upstream side) and a lot of anglers miss this trout which is unfortunate because it could very well be the largest trout located around the boulder. The upstream side of the boulder provides a number of significant advantageous to a trout. First, the current here does not just slam into the face of the boulder, rather the boulder 'pushes' back against the current and forms a cushion of softer water (which is designated by the dashed semi-circle in figures 1 and 2). This cushion of softer water forms an area that trout can hang out in and feed without expending excessive energy.
Second, the trout in this position has a clear view of any food traveling downstream since it will have more of an unimpeded line of sight than if it was stationed behind the boulder. Also, more food can be brought to the trout before the current is split around the boulder. Third, this cushion of water also makes it a safe spot for trout to stay out of reach from predators; nothing can attack the trout from behind, aerial predators will struggle to see the trout (or may not risk diving right next to a boulder), and if the trout feels threatened it can quickly dart into the surrounding faster current.
The trout on the upstream side of the boulder could be located close to the river bottom or the surface. It all depends on the size of the boulder, the force of the current, and what the river bottom is comprised of. Most often, the larger the boulder the larger the cushion, and this permits the trout to hold nearer the surface.
Where Trout Position Behind A Boulder
As the current passes the boulder it splits and forms two tracks of water downstream of the boulder. Immediately behind the boulder is a turbulent eddy where water is forced into multiple directions (this is designated as white arrows in figures 1 and 2). This is actually one of the least productive places for a trout to station themselves in. The swirling, chaotic water makes it difficult for trout to remain in place and locate food as it is tossed by. Only if the boulder is quite large, and forms a more gently eddy/pool in its wake, would it be worthwhile to cast your flies into.
A few feet further downstream, the eddy begins to meet the current and forms a channel of water that flows in one direction. The water will still look a little choppy on the surface but it provides a much better channel for trout to hold in because the water will be flowing in a unified direction and is slower than the faster, outside currents.
In figures 1 and 2, the two trout downstream of the boulder are located in this channel. These trout are taking advantage of the slipstream formed off the boulder and can dart at food as it passes by in the faster, main current. Troughs can also be dug out in the boulder's wake which provide further relief from the current for a trout. This feeding lane can be 3-5 times the length of the boulder before it merges with the main current of the river and picks back up in speed.
Trout Located to the Side of a Boulder
A third spot that you may find trout is on the side of the boulder, and this can be another harbor for large trout (figure 3). An ideal situation is where a boulder has a ledge, or piece, that sticks out into the current and creates a pocket of soft water that allows a trout to stay beneath the overhead current. Again, the trout here has a prime opportunity to snatch food as it passes around the boulder, and it is well-protected.
It can be difficult to know if there is a ledge on the side of a boulder that forms a pocket of soft water, but one of the signs is a trough of darker/slower water visible along the boulder.
How and Where to Present Your Flies
A single boulder offers numerous spots to present your fly, and it may take a dozen or more accurate casts to effectively cover the entire zone. First, we'll cover how to approach a boulder from downstream, this direction means that the trout will be facing away from you and gives you a greater chance to stay out of their line of sight. When fishing this way, a dry-dropper can be a very effective set-up to use.
(Read: What is a Dry-Dropper Rig?)
(Read: 3 Ways to Create a Dry-Dropper Rig)
The first series of casts should be at the tail-end of the channel of calmer current. Progressively work the flies up this channel making casts inside the lane and along the seam that forms in-between the fast, main current and the slower channel of water.
Next, you will want to target the side of the boulder. Quite often, a trout that is located here is beneath some pretty strong current, so using a weighted nymph can be the best option for hooking into it. Dry-dropper, indicator, and euro nymphing rigs all work well, but the important thing to keep in mind is that you will want to land your flies upstream and allow the nymph(s) to get to depth and then drift them very close to the boulder. At times, my indicator or dry fly will brush against the boulder, and that helps to confirm that my suspended nymph is getting close to where that trout could be.
The third place to target is the upstream side of the boulder. When targeting the upstream side of the boulder, I prefer to be standing upstream or quartering-upstream of the boulder. This direction helps to mend line more easily or to pay out slack and allow the flies to drift down towards the boulder. Again, a dry-dropper is a great rig for this situation, but make sure you do not pull your flies out too soon. Often, once the dry fly (or indicator) is about to collide with the boulder is when the nymph has just reached the trout. To help visualize this, look at figures 4 and 5:
Swinging wet flies or streamers is another good way to target the front side of a boulder. You can either cast directly at the boulder and then slowly work the fly closer to the boulder, or you can cast at a quartering angle and then swing the fly towards the boulder. Sometimes it may pay to hold the fly there longer than you think which could be just enough to elicit a strike from the trout.
(Read: Wet Flies: Tactics and Techniques for Multiple Fish Species)
(Read:How to Use Wet Flies - Rigging)
Common Mistakes When Fly Fishing Around a Boulder
Dunking Flies into the Back Eddy
This is a very common mistake anglers make because we think the eddy looks like a good spot for trout. Yet, as we discussed above, it can be way very chaotic place for a trout. Unless the boulder is very large and creates a sizeable pool in its wake, the eddy is best avoided. Even if we know this, our flies may still get sucked into the eddy (figure 6), and in this case it is best to just re-cast and land them into the calmer channel of water formed downstream of the eddy (figure 7).
Landing flies into two different currents
When landing flies into the channel downstream of the eddy (and when using a dry-dropper or indicator set-up), the flies may land or get pulled into two different currents. This happens when our dry fly or indicator lands into the calm channel but the nymph lands into the surrounding faster current (figure 8) or vice versa. The nymph will then be ripped downstream pulling the dry fly along with it, ruining the drift.
Another situation is when we see our dry fly or indicator land into the calmer channel but it stalls out. What usually happens in this case is that the nymph has probably landed into the back eddy and is now just swirling around and preventing the dry (or indicator) from drifting (figure 9). In this situation, you should be able to pick the line up and pull the flies downstream to get the nymph out of the eddy.
Also, the key to avoiding those mistakes is take your time with your casts and pay attention to where the flies land. Using a tuck cast is an excellent way to help keep the flies (or indicator and flies) all in the same current lane. A tuck cast can turn the leader over quicker and kick the flies downward rather than straight out as in a normal cast. The tuck cast will also help the flies to plunge into the water and get to depth faster which is very useful when fishing pocket water.
(Video: How to Tuck Cast)
Landing the Flies Too Close to the Front Side of the Boulder
In order to drift our flies close to the front of the boulder (and allow the nymph to get to depth), we need to land them well upstream of the boulder. I often see anglers that land their flies barely a foot in front of the boulder and within the blink of an eye the flies are swept around it which hardly gives a chance for the trout to see or take them. So, be sure to land your flies several feet upstream to not only allow the nymph to get to the depth but to also help the trout to see them coming (figures 4 and 5).
Failure to Mend the fly line
With so many currents traveling at different speeds and directions it is difficult to keep the fly line and leader from affecting the drift of the flies. This is a pretty big topic and it is covered in Part 3: How to Fly Fish Pocket Water: Casting, Mending, and Line Management
Fly fishing in pocket water can involve a steep learning curve, but as challenging as it can be it is my favorite piece of water to fish. There are innumerable feeding lanes and hiding spots for trout, and trying to think about the hydrology that is weaving around just one solitary boulder can make your head spin. Hopefully, this article and illustrations have provided some insights into what is going on under the surface and will help you enjoy your time fly fishing some pocket water this season.
Again be sure to check out more articles from the Reading Water Series:
Reading Pocket Water Part 2 here: How to Fly Fish Pocket Water: Rock Gardens
Reading Pocket Water Part 3: How to Fly Fish Pocket Water: Casting, Mending, and Line Management
Reading Riffles: Improve Your Skill at Reading Water for Fly Fishing: Riffles
Lastly, if you live in or are visiting Spokane, I provide guided fly fishing trips and instructional lessons around Spokane to include float trips on the Spokane River and stillwater trips across various Eastern Washington lakes. I guide with Fly Fish Spokane, and more information/trip rates can be found at the website: FlyFishSpokane.com