Whether you’re a whitewater rafter or fly fishing enthusiast, it’s essential to understand what a river eddy is, how to identify them, and how they affect your rafting path or fly fishing success rate.
In this article, we will unpack the basic information about river eddies.
Let’s start by discuss what a river eddy is.
What Is A River Eddy?
A river eddy will be located immediately downstream of an obstacle in a river, such as a rock or a boulder. When water passes by the obstacle, it naturally seeks to backfill the lower-pressure area behind the rock. This phenomenon effectively creates an upstream current, flowing in the opposite direction from the primary current. In this river eddy diagram, you can see the upstream facing yellow arrows, indicating downstream water is backfilling the area behind the rock.
This event forms an upstream current, opposing the natural flows of the downstream current.
Eddies are found throughout rivers with rapids as well as calmer rivers like small backcountry trout streams.
How Large Can A River Eddy Be?
A river eddy can range in size from only a few feet wide to the size of a football field. Their magnitude depends on the size of the obstruction, the width of the river, and the amount of water flowing through it.
In most whitewater and fly fishing rivers in Colorado, eddies are generally no larger than a school bus but often much smaller. In backcountry creeks and streams, they are about the size of a VW Bug or smaller.
These river features are important to understand for people rafting just as much as for fly anglers. When rafting, river eddies often provide a place to re-group with other rafts.
When the currents in an eddy are extra strong, rafters try to avoid entering it, as this can sometimes get them stuck.
In fly fishing, these features can provide an excellent place for trout to hold. Smaller eddies in streams where trout may live will have mellow currents and a steady food supply. As such, small stream eddies are prime locations for anglers to fish.
It’s important to note that trout in an eddy will be facing in the general downstream direction, as opposed to upstream like its trout companions holding in the main current. This is because trout are generally always facing into the current when food can easily drift by their mouths.
Understanding River Eddy Currents
When water attempts to backfill the space behind an obstacle, the current will flow in the opposite direction from the primary current. There are three primary zones within an eddy.
- Filling Zone: Where the water initially begins back-filling the space behind the obstacle
- Standing Zone: Where water is relatively still, generally in the middle of the eddy
- Flushing Zone: Where the eddy current re-joins the primary current of the river.
The standing zone is often an easy spot for whitewater rafters to re-group. It can also be a location where trout are holding, although most often a trout will be holding closer to an eddy line.
The filling zone often has the strongest currents within an eddy. It begins at the bottom of an eddy (the part furthest downstream) and ends at the top of the eddy (the most upstream part closest to the obstacle).
Due to centrifugal forces, the perimeter of the eddy often has the strongest currents, while the standing zone has the most mellow currents.
The flushing zone of an eddy is where its current mixes back in with the main river’s current. In fly fishing, this zone is also known as a tailout. We like to fish in tailouts in the middle of the summer and early fall when fish are spread out and have no problem holding in medium-speed currents.
What Is An Eddy Line?
Eddy lines are where the downstream flow of the primary current meets the upstream flow of the eddy’s current.
Eddy lines are fun to paddle in but require skill to maneuver through. Some lines in the largest rivers can be large enough to violently move a raft or even flip it. However, these types of eddy lines don’t exist in most western rivers.
In fly fishing, we recommend that you drift your flies on either side of an eddy line to float your fly past a holding trout.
Casting directly INTO an eddy line is generally not recommended, as conflicting currents can disrupt your drift. Instead, pick your current and commit to it throughout your drift.
Are Eddies Dangerous?
A river eddy is not inherently dangerous. However, anyone who recreates on a river should understand how an eddy works.
River sports enthusiasts most often consider eddies their friends. An eddy provides a break from the mainstream flow, offering people an opportunity to regroup.
However, eddies can be challenging to escape from on the most significant rivers during high flows. Those you can’t escape from are called “keeper eddies.” Although relatively uncommon, keeper eddies can be dangerous.
The video below shows the power of one of the more famous and violent eddies, the Room of Doom on the Colorado River in Westwater Canyon. Make sure to watch til the end!
Small eddies in mellow currents are typically not dangerous, although they can be stronger than they look.
No matter what, stream flows in the primary current or in an eddy can be very strong and demand respect.
We recommend any river enthusiasts do plenty of research on the place they’re recreating before they go, learning if there are any dangerous eddies and rapids in the river.
Are Holes In A River The Same as An Eddy?
A hole in the river is not considered an eddy, but it is formed by similar concepts and streamflow dynamics.
When water flows over a rock, the water dives to the bottom of the river. The void downstream of the rock is then backfilled with water. This is comparable to how an eddy works, but involving gravity pulling the water towards the river bed rather than downstream.
If you can picture it, a hole resembles an eddy rotated 90 degrees towards the sky.
What Does a River Eddy Look Like?
Visualizing these river features is best done by looking for places where leaves, foam, or sticks appear to circle back upstream or collect in a pool.
Unlike the forward-charging river, these pockets of reverse-flowing water create a visual contrast to the main current. Eddies are generally calmer parts of the river and don’t have rapids.
The Significance of Eddies in Rafting
River eddies play a crucial role when white water rafting.
Catching an eddy (aka entering an eddy to take a break) and exiting one is an essential rafting skill that should be practiced.
When something goes wrong on the river (e.g., someone falls out of the raft), it’s crucial for the captain to quickly navigate the raft into an eddy.
Because most eddies are friendly places to re-group, they are also good places to execute a rescue plan when someone takes a swim.
“Catching an eddy,” aka entering an eddy, involves careful planning of position, angle, and speed. The video below provides a detailed explanation.
Not only will rafters want to know how to catch an eddy, but they should know how to exit one. Completing this task can be easier said than done in the rivers’ most violent, strong eddies.
As a general rule of thumb, the smaller the eddy, the harder it will be to catch and the easier it will be to exit. Conversely, large ones can be challenging to catch and exit.
Practicing your eddy-catching skills is one of the most important things to learn when rafting or whitewater paddling.
What Does “Eddy-Out” Mean?
When someone in your group says, “Let’s eddy-out,” they are telling you they want to catch the next eddy.
Since it can be challenging to verbally communicate on the river when the sounds of rapids drown out your voice, using a sign language signal is a good skill to have.
The sign language signal for eddying out is raising your hand above your head and moving it in a circular motion. Do this until someone acknowledges the signal and responds with a signal indicating they understand.
Fly Fishing Back Eddies, Pocket Water, & Tailouts
Fly fishers typically fish in rivers with enough features to help fish hold in place. These areas are referred to as back eddies because the current reverses direction and flows upstream.
Back eddies are a place where food can gather into a slower current, making meals easier for trout to find. In many of the larger back eddies, clumps of foam will form on the surface, providing cover for trout to feed beneath the surface.
One of our favorite sayings is, “Foam is Home.” Find the foam, and you’ll find a trout.
Anglers often encounter plenty of micro eddies in a stream, which can indicate where a trout may be holding. A micro eddy is one that is generally no larger than a bushel of corn, say 3 feet x 3 in diameter, although sometimes smaller.
Eddies in smaller trout streams will be abundant, and require the fly fisher to accurately cast into a small zone to find the fish.
Pocket water is associated with rivers with protruding boulders throughout a section. When water passes by the boulder, a micro eddy is created on its downstream side.
Just downstream of the eddy, a Y-shaped “pocket” of slower-moving water will form. We also sometimes call these pockets tailouts.
Trout like to hold in these pockets or tailouts because the water moves slower than the main current, allowing them to feed without exuding too much energy.
Trout will face into the current wherever they hold, meaning trout in an eddy will face in the general downstream direction but into the eddy’s current.
When fly fishing, we advise anglers to look for river features such as eddies, pocket water, and tailouts for locations trout may be holding.
Conclusion
River eddies are one of the main features you will encounter when rafting or fly fishing. They can be found everywhere and vary in magnitude depending on the stream flow and the size of the obstruction.
While it’s important to know what eddies look like and how they work, it’s equally as important to understand how to use them for your benefit when rafting. And when fly fishing, to understand how an eddy affects a trout’s holding pattern.
Feel free to contact us at Slackwater at info@slackwaterco.com for more information or other rafting/fly fishing tips. Thanks for reading.