Dry Fly vs Nymph: How to Choose on the Water
Watch one lane, name the layer the trout are eating in, and tie on one fly to test it.
From the book Fly Fishing for Nerds — $9.74 →
A dry fly floats. A nymph sinks. Maryland DNR states that difference directly: flies that imitate the aquatic stage are nymphs, and the adults are imitated with dry flies because that stage floats on the surface. The choice on the bank is which of those the trout in front of you are taking. A hatch chart for the month is a guess you have not checked.
What you need
A Parachute Adams for the mayfly row, an Elk Hair Caddis for the downwing row, a bead-head Pheasant Tail for the quiet surface, and 5X for a small dry.
- Parachute Adams, sizes 12–18 Flies Direct
A dozen parachute Adams, three each of sizes 12, 14, 16, and 18. The post is there so you can see the drift.
- Tan Elk Hair Caddis, size 16 The Fly Fishing Place
An elk-hair caddis. Buoyant enough for evenings and for pocket water. The Amazon link is a six-pack of tan size 16.
- Bead-head Pheasant Tail, size 16 Region Fishing
A dozen flashback bead-head Pheasant Tails, hook 16. The bead is the weight, so start without split shot.
- RIO Powerflex tippet, 4X–6X RIO
Three 30-yard nylon spools: 4X, 5X, and 6X. 5X is the usual small dry. 6X is a size 18 in clear water.
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1. Watch one lane before you open the box
Stand still for two minutes. You are looking for where the food is being eaten, not for a fly name.
Maryland DNR’s marks do not require a Latin name. A trout flashing on the bottom, or in the water column, is taking nymphs in the drift. A trout splashing or slurping at the surface is taking adults, or nymphs as they come through the film. DNR also says trout are feeding on drifting nymphs most of the time, year round, and that this is a good place to start. Use that when the surface gives you nothing to match. It is a starting hypothesis, not a promise that this run will eat.
Tom Rosenbauer, in the hatch chapter of The Orvis Fly-Fishing Guide, separates a surface meal from a fish that only looked like it rose. Find one fish rising steadily. If a bubble is left after the take, it ate something on the surface. If there is no bubble, and the flies floating over its head stay untouched, it is probably taking emerging nymphs just under the surface. A splash that launches a mothlike fly into the air is the other caddis mark in that chapter: the fish chased a pupa and was late. Rosenbauer’s instruction is to put the dry away and fish a pupa just below the surface.
Those are different observations. A ring on the water is not, by itself, a reason to tie on a dry.
2. Pick one row
| What you see | What you tie on | What counts as the test |
|---|---|---|
| A deliberate rise, a bubble afterward, insects on the water | A dry fly the size of an insect you can catch | The fly drifts with the foam and leaves no wake |
| Rises with no bubble, or a fly that pops out of the splash and flies off | A nymph or pupa just under the film, or a dry with a short nymph under it | The dry does not skate. The nymph is only about a foot down |
| Splashy rises to bugs fluttering on the surface | A downwing dry, such as an elk-hair caddis, sized to those bugs | The same dry-fly test: no wake, and a handful of clean drifts |
| Flashes under the water, or a quiet surface and no insects | One nymph, fished near the bottom | The indicator tracks the bubbles. Change depth before you change flies |
| Grasshoppers or ants in the grass, and the holding water is against that bank | A dry, along that edge only | You fished the edge because you saw the bugs, not because the month sounded right |
Rosenbauer’s fluttering case is its own row. Bugs kicking on the water, usually caddis, call for a downwing dry of the right size. That is not the same as a fly that escapes the rise. If you did not see which one happened, you do not have the observation yet. Watch another minute. The same loop as the observe page: one thing you saw, one sentence about the layer, then a short test.
3. Run the dry
Catch an insect if you can. Size first, then shape, then color. A Parachute Adams is the visible mayfly in the starter box. An Elk Hair Caddis is the downwing when the bugs look like caddis. The Pheasant Tail is the nymph for the other rows. Those three are on the gear page.
Cast upstream of the rise so the fly arrives on its own. If it cuts a wake, that drift did not test the pattern. It tested drag. Mend, or pick up and cast shorter. Maryland DNR’s shorter cast is about 30 feet, with the rod tip holding line off the faster current. A handful of drifts that actually float is the trial. A dozen wakes are not.
If the dry sinks, you did not test a dry. Maryland DNR dresses the fly and the leader with a paste or powder floatant so they stay up. Do that, or tie on another dry, and repeat the same drift before you call it a refusal.
If rising fish refuse a dry that matches the bug in your hand, leave the rest of the box closed. Rosenbauer writes that a refusal often means the fish does not want a fly floating that high. The next trial is a nymph a short distance under a dry. The indicator guide already sets that length: about a foot, or a foot and a half in slower water. Longer than that and the dry skates, and you have tested neither fly.
Tippet for a small dry is usually 5X. The tippet guide is what the X number measures, and how long a piece to cut. Change the tippet because the drift needs it, not in the same minute you change the fly.
4. Run the nymph
When the surface is quiet, this is the same opening as the no-hatch guide: one Pheasant Tail, one depth, one lane you already chose while reading the water. The indicator guide is where the float goes and what a take looks like. Give the lane a handful of drifts that track the bubbles. If they are empty, lengthen or shorten before you switch to a dry because the dry is easier to see. Easier to see is not an observation.
If fish start to rise while the nymph is on, stop. The row changed. Match the bug if you can catch one, and move to the dry row or the short-dropper row. Write that the hatch started.
Two changes in one drift — a new fly and a new depth — leave you unable to say which one mattered.
5. When the river is high, stained, or cold
High, stained water is a different problem. A small dry is hard for you to see, and hard for a trout to find, and the soft edge is where a fish can hold. The after-rain guide is the fly for that hour: something larger and darker, close to the bank. The quiet-water nymph on this page is the wrong default on a river you cannot see into.
Cold water shortens the feeding window, and most of that feeding is often under the surface. Stay with the nymph, deeper and slower. The water-temperature guide is what the thermometer means at both ends of the year, including the summer stop near 68°F.
6. Write the layer down
One line: dry or nymph, what you saw (bubble, splash, flash, or nothing), the size, and whether the drifts were clean. After a few trips the note shows whether you fish a dry on every river because you like to watch it, or only when a fish left a bubble.
Choosing the layer, and then the drift, gets more room in Fly Fishing for Nerds: A Data-Driven Guide to Finding, Hooking, and Landing Trout. Readers can take 25% off ($9.74) with code NERDS25 at https://leanpub.com/flyfishingfornerdsadata-drivenguidetofindingfishfly-fishing-for-nerds/c/NERDS25.
The Riverbank Checklist is the one-page routine for the bank before you tie anything on.