This article is part of a Reading Water Series. Be sure to check out Part 1 (Targeting Trout Around a Single Boulder), where we explore the unique hydraulics created by a single boulder and where trout position themselves around it. This article will build off of what we discussed in that previous post by looking into the more complex hydraulics that multiple boulders form.
Also check other articles in the Reading Water Series:
What Is a Rock Garden and Why Should You Fly Fish the Pocket Water Within a Rock Garden
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.
The area in a river or stream that is commonly referred to as a "rock garden" is where numerous boulders form a medley of seams, pools, eddies, lanes of slower current, plunging water, and so on. We will explore this unique habitat and analyze where trout station themselves within it.
A stretch of 20-30 yards of river that is strewn about with boulders could hold scores of trout. All of those boulders form a rock garden full of ideal spots for trout to hold and feed, and it is an absolute thrill to methodically pick your way through and catch trout in surprising places.
Trout in pocket water are also opportunistic and will more readily go after food before it swept downstream of them. This is great for anglers because we do not have to concern ourselves with precisely matching the hatch, and we can also use larger dry flies to grab the attention of any nearby trout.
A small stream in the mountains or hills can be entirely comprised of rock gardens, and it is an enjoyable place to either learn about fly fishing or to take someone and introduce them to the sport. Watching a spunky trout crash into a dry fly floating on the surface can excite and bring out the kid in just about any one of us!
Effectively fly fishing these rock gardens, however, requires some knowledge and skill with reading water. Plenty of fly fishers pass over rock gardens because it looks like a cacophony of turbulent and unpredictable water. Therefore, the goal of this article is to provide insights that you can use on your local waters in order to help build your experience and ability at fly fishing pocket water within a rock garden. The more knowledge and on-the-water experience you gain the more you will find yourself gravitating to this type of water, it is just that much fun!
Pocket Water: Water Temperature to Keep An Eye Out For
On rivers and larger streams, trout typically inhabit pocket water when the water temperature climbs above 52°F. Above 52°F, a trout's metabolism really kicks into gear and they start to require more food and oxygenated water. Pocket water is a great source of insects and the churning currents provide well-oxygenated water. A lot of anglers refer to pocket water as "summer time water" and focus their attention on it because that is where the trout begin to shift to in the warmer months. So, be sure to bring along a thermometer with you in order to take a water temperature reading to help determine if trout could be pocket water.
Lower water temperatures will cause trout to seek out calmer water like pools and deep runs. However, on creeks and small streams in hilly or mountainous areas, trout may stay in pocket water because that is all there is, but they will most likely be in deeper pockets when the water temperature is cold.
*Side Note- When water temps climb beyond 67°F, it's best to stop fishing because the trout go into survival mode.
Rock Gardens: Common Elements of "Trouty" Water
Pocket water found in a rock garden is highly variable, but trout are not randomly distributed throughout these rough waters. Rather, they gravitate to particular spots where they can feed with some level of protection. These "trouty" spots have common elements that you can find on most rivers/streams that have rock gardens.
Each element is an insight into where you might find a trout. We will go through each of them below and provide some illustrations that will help to improve your skill at reading water. Even if you are going to fly fish a new river, or new stretch of river, these common elements can provide a basic starting point that you can use to begin your day.
Seams Between Fast and Slow Currents
Rock gardens carve up a river's fast current into numerous channels of slow and fast water. Trout seek out seams between fast and slow currents because it provides two things for them: the slow current gives them a spot to hold in without expending excessive energy, and the fast current delivers food to them (figure 1).
If you are targeting a seam, try to land your fly or flies right on the seam or just inside the slower water, this is especially true if you are using a dry fly or dry-dropper rig. This will help to keep the dry fly from being submerged and will give the trout a chance to take your fly.
Uniform Direction of the Current
Boulders in a rock garden produce eddies and whirlpools where the river's current is turned around or forced into multiple directions. Turbulent current that flows in unpredictable directions is an incredibly difficult spot for trout to hold in, and food is also tossed around making it hard for them to grab it. Instead, trout will try to find current that has both a predictable and consistent direction of flow.
When you look at a rock garden, take a moment to find where the current is flowing in a uniform (and slower) direction (figure 2). Areas that have chaotic, directionless currents will look like a washing machine on the surface.
This does not necessarily mean the current is flowing downstream. In fact, places behind some boulders can create calmer currents that flow back upstream and are easy for trout to station in. Just note, a trout in this spot will be oriented in the current looking downstream (this can be seen in figure 2 with the trout that is stationed behind the boulder along the right bank).
Large, relatively calm pools/eddies can also form behind bigger boulders which is a good place to land your fly. Trout can hold in these pockets because it is less turbulent, and they can nab food drifting in the nearby current or in the pool itself. A characteristic of these pockets is a more placid surface that provides you with a "window" to look through and see the river bottom below (as opposed to the chaotic surface water behind smaller boulders).
As the current is funneled between boulders it can gouge out deeper channels of water. Pools and eddies behind the boulders can also have increased depth. Looking at this from the river bank, deeper areas will appear darker or bluer in color.
For a trout, deeper water can provide additional protection from overhead predators, and they can also hold closer to the river bottom to stay out of the faster current above. Deeper water can be productive areas to cast your fly into. However, if there are standing waves roaring over a deep channel of water then it may be too hard to get your flies to depth to where trout are holding close to the bottom (if there are even any trout holding beneath those stronger currents).
Many anglers may have heard the phrase "foam is home" and that you should cast your fly into the foam. For the most part that is true, and it is a good place to begin prospecting for trout. Foam lines can tip you off to where currents are converging together and thus where food is being funneled. Trout position under or near those foam lines and pick at food as it passes by (figure 3).
Some of the best foam lines are actually pretty subtle, and they are typically further downstream of where the faster and slower currents converge.
Foam can also be seen in slack pools or eddies behind larger boulders (or in front), and at times large pillowy bubbles will stack up in those corners. While these are not "foam lines" they are places that can be worthwhile to cast a fly near. However, there should be sufficient current nearby, because some of those slack areas are just too far away from the current and the food it delivers.
Along the Bank
Plenty of anglers look past spots that are right along the bank because they are trying to find trout further out in the river/stream. Yet, the bankside can hold trout as well because it creates friction against the river and slows the current down. While the bankside provides a calmer area for trout to hold in, they still need protection. Overhead cover (like a tree limb) or some water depth could be all they need.
The bankside is also a great spot to focus on when there is high water due to runoff or when a heavy rainstorm passes through. The heavy, faster current will still be slowed when it runs up against the bank, and this offers some relief for the trout.
On many riverbanks that run along roadsides, you might notice boulders or concrete blocks placed there to prevent erosion, this is termed "rip rap." Rip rap has ample nooks and pockets for trout to nestle themselves into, and even on fast outside river bends rip rap can break the current up enough to provide cover for plenty of trout. Again, during run-off or other high-water events, targeting areas with rip rap is a good tactic.
Overhead cover (like tree limbs, bridges, undercut banks, etc.) is additional insurance for trout against avian predators. Log piles can also be overhead cover for trout. These piles mainly stack up on the upstream side of boulders, so drifting a streamer or wet fly into one of these pockets could produce a nice trout.
Tree limbs can also provide additional food for a trout when terrestrial insects climb out onto the branches and then fall into the water. On smaller streams where terrestrial insects make up a larger portion of a trout's diet, casting a large dry fly near tree limbs can be very rewarding.
Plunge Pools and Drop-Offs
In mountainous or hilly terrain, small streams are characterized as being "high-gradient streams." What this means is that as the stream flows down the mountain/hills it loses elevation quickly and so the slope (or grade) of the stream is quite high. If there are plenty of boulders in a high-gradient stream, then you will have plunge pools.
Plunge pools are where the stream pours over the boulders which can form a pool at the base of it. These plunge pools are fantastic places for trout to school up in and feed on anything that comes over the little waterfall.
On rivers and larger streams, there may be a lack of plunge pools because the river is not flowing through such steep terrain. Rather, you may find drop-offs where the river flows over a submerged boulder and creates a calmer pocket of water on the downstream side. Typically, there will be a lack of an eddy because the current is still flowing over the boulder, so tossing a fly right into that pocket is worth the cast.
Drop-offs can also form when there is a band of submerged rocks and boulders that cut across the current (figure 4). Typically, there will be a decent amount of white water and foam as the water passes over the boulders with deeper water immediately downstream. Instead of casting your dry fly right into the foam (which will cause it to sink), land it right where the white water starts to fizzle out.
Front and Sides of a Boulder
The front and sides of a boulder are two other common elements of "trouty" spots in pocket water. I discussed this in detail in our previous article: Targeting Trout Around a Single Boulder
Any of these common elements can be spots to find trout, but combining them together is when you can discover some true gems. That foam line along the bank flowing over some deeper water with a tree branch overhead... Yeah, that could be a prime feeding lane with a lunker in there!
The key is to pause and take time to read the water. Spending just a minute looking at the water can reveal clues and secrets that many anglers scan past. Also, with each trout you hook into (or that at least rises to your fly), ask yourself: Why was that trout there? The more you do that, the better you will become at reading pocket water.
Below are a few scenarios that we will go over that further demonstrate where trout can be found in pocket water amongst rock gardens. In a future article, we will cover tips on casting to these trout, mending your fly line, and improving line management skills.
How to Read Pocket Water, Scenario One:
In this scenario, the trout in Spot A are located just downstream of a series of submerged boulders where the current is flowing over top. The boulders have created some nice drop-offs and deeper water immediately downstream which helps to funnel food straight to these trout. Notice how the trout are not right in the foam but a little downstream so they can see food drifting to them.
The trout in Spot B is tucked to the side of the large boulder which is buffeting the strong current. The boulder is near the swift current in the middle of the river, and plenty of food drifts by this trout.
In Spot C, this trout is located in the pillow of softer water right in front of the boulder (depicted by the dashed semi-circle). The current has been slowed down by the boulder in Spot B, and this creates a gentler current that carries food right to the trout in Spot C. This trout has a great position and can easily watch food drifting down to it.
Finally, the trout in Spot D is further downstream of the boulder at Spot C. This trout is further back to avoid the more turbulent eddy behind the boulder. It is positioned near the seam that separates the fast current from the slower current where it is swimming. There is also a nice foam line that shows where food is being funneled over the trout.
How to Read Pocket Water, Scenario Two:
In Scenario Two, the trout at Spot A is positioned in front of a partially submerged boulder. The river's flow is calmer here because the large boulder upstream has dissipated much of the current's force. Food is also brought right by the trout before it is funneled through the band of rocks behind it.
In Spot B, this trout is in a calm pocket right next to the where the main current is funneled through the rocks. There is some depth here as the water is funneled, so the trout can also hold closer to the bottom to stay under the swift current. On the other side of the funnel in Spot C, there are a couple trout that have taken positions downstream of some drop-offs. These drop-offs are formed by the submerged rocks upstream of the trout. These drop-offs have also carved out some deeper water for the trout to hold in.
The trout in Spot D is holding in a calm pool next to a big boulder that has deflected the main current. This prime spot has lots of food drifting by and the boulder offers additional protection for the trout. In Spot E, the main current has slowed down and a nice foam line shows where the majority of food is flowing. There is a deeper, calmer channel here, and the trout can hold lower to the bottom and easily tip up to grab any passing food. There is not as much protection here for the trout, but the water depth adds some security and there are nearby boulders that the trout can escape to.
How to Read Pocket Water, Scenario Three:
In this last scenario, let's assume it is late summer or early fall and the water levels have receded. These lower flows will force trout to seek out main channels of water, and deeper ares of the river/stream for both protection and food.
We can see a huge boulder at the top of the image near the left bank. This boulder slices through the main current and forms a large pocket of smoother water downstream (Spot A). There is a tree that is hanging over this large pocket of water and a trout is under its branches. The calm pocket of water is easy for the trout to swim in, the main channel of the river delivers plenty of food, and the tree branches provide overhead cover. This is a prime spot.
Further out into the river and closer to the right bank, the river shallows out before it runs into a band of boulders. Let's assume the water here is very shallow (just a few inches) and rough, so it provides little in the way of protection or even space to maneuver around in. At the band of boulders there is a little more depth to the river but nothing significant, a couple pockets here might hold a small trout or two. Downstream of the boulders, the current again shallows out and slows way down; this would be a poor choice for a trout due to the lack of protection and any food being delivered via the current.
Back on the left bank of the river, the main current funnels past boulders on the bank. These boulders along the bank break the current up and create pockets for trout to hold in like the trout in Spot B.
As the current funnels past the boulders, another trout in Spot C is positioned beneath the foaming current where there is still decent water depth. Just downstream, in Spot D, the main channel slows down and a nice foam line forms. It is still a deeper channel of water and there is enough food drifting through it for the trout to feed on.
Pocket water in a rock garden is a cacophony of turbulent currents, and looking at from the bank it can be difficult deciphering where a trout might be. The article and illustrations above can definitely provide a starting point when you approach pocket water, but again the best tip is to pause and read the water before sending your fly into the current. By taking the time to look at and study pocket water, you will begin to intuitively sense which spots feel "trouty" amongst all of the boulders and tumbling water.
Again be sure to check out more articles from the Reading Water Series:
Reading Pocket Water Part 1 here: How to Fly Fish Pocket Water: Targeting Trout Around A Single Boulder
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