Eddy is a term used in the physical science of fluid dynamics to describe the swirling and reverse currents associated with moving fluids (i.e. air, water) as it passes over and around an obstructing object, back-filling the void space behind or downstream from the object with a characteristic swirling current counter to the main current’s forward direction.
In a river environment, eddys (sometimes spelled “eddies”) are quite common and generally occur in the space downstream from or “behind” large exposed rocks, boulders, and partially submersed detritus such as fallen tree limbs and other debris, either natural or man-made.
Eddys are often observed in river environments as the gently swirling, slow moving areas between between point bars and main channels. Eddys can also be created near severely undercut banks where localized reverse currents tend to create an “eddy-like” effect at the water’s surface.
To the fly fisher, an eddy is an important component of a river, stream, or even lake environment. Insects will be trapped in the main current upstream from an eddy either as struggling nymphs or emergers, or as spent adults called spinners. As the main drift nears the eddy, it collects these insects and when it reaches the eddy, the water is usually loaded with “pre-packaged” meals for hungry trout. Because trout food tends to collect in the “lazy-susan” reverse currents of an eddy, fish often hang out in these areas, waiting for the next morsel to slide gently into their feeding lane.
Feeding trout love eddys and subsequently fly anglers have learned to love them as well. Presenting a nymph or visible dry fly on a dead drift that passes through an eddy can be an incredibly effective method for hooking large fish in good numbers throughout the day of fly fishing.
When reading a river or stream, look for large exposed rocks or submerged logs and you’ll probably spot an eddy. In a lake environment, look for eddys near the mouths of rivers that feed the lake, along shorelines with rocks and debris where a consistent long-shore drift is prominent, and on days when winds are high and shorelines are subjected to stronger currents.
After identifying an eddy as a potential fishing target area, the approach becomes very important. Because eddys tend to have moving water, fly anglers are often inclined to approach very closely, but because eddys also tend to be shallow and of decent clarity, a clumsy angler can spook fish in an instant. Stalking is a practice every great fly angler will practice regardless of the water she casts to, but when approaching an eddy caution and stealth are paramount to successful fishing.
Eddies can occur on just about every type of moving water, from small to large. Even if you’re fishing an eddy occurring on a larger river, remember, you’re just fishing the eddy so treat it correctly. The best approach might be to fish your eddy like you’re fishing a spring creek, where your presentation need to be very subtle. Longer, lighter leaders help for sure and having the correct fly rod for the job doesn’t hurt. To maximize your efforts we recommend two fly rods perfectly suited to fish eddies.