A reach cast decides where your line lands relative to the fly. Slack line casts decide how much line lands and what shape it is in.
They are the other half of the same problem, and they are the ones people reach for when the current is complicated enough that no amount of positioning the line sideways will save the drift.
They also come with a cost that almost nobody mentions, so we will start there.
Slack buys drift and costs contact
Every foot of slack you put in the line protects the fly from the current for a moment longer. Every foot of slack is also a foot that has to be removed before anything you do with the rod reaches the hook.
That is the whole trade, and it is a real one. Fish a heavily slacked line and you will get beautiful drifts and miss takes, because by the time you lift, the rod is still gathering line that was lying in curves on the water. Fish a tight line and you will feel everything and get four feet of drag-free drift.
The skill is not maximizing slack. It is putting in exactly as much as the drift requires and no more, in the place where the current will use it first.
Anyone who has watched a good angler fish a dry fly downstream has seen this. The slack goes in deliberately, it is measured, and the moment the fish eats, they know precisely how much line they have to move before the hook does anything.
Drag Is Killing Your Drift: Start With Your Casting AngleThe pile cast
The simplest and the most extreme.
Aim the forward cast high, well above the water, and stop the rod high. The loop turns over in the air, runs out of energy, and everything drops more or less straight down. The leader and the front of the line land in a heap around and behind the fly.
That heap is your slack, and it is concentrated exactly where you want it, near the fly rather than out by your rod tip.
This is the cast for a downstream presentation, which is otherwise the hardest drift in fly fishing. Casting downstream, the current immediately begins pulling your fly back toward you, and a straight line gives you almost no drift at all. A pile cast gives you several feet of the fly floating freely while the current straightens the pile out.
The costs are accuracy and contact. A pile cast is imprecise by nature, and you have deliberately created the maximum possible distance between your rod and your hook. Set gently and late.
The S cast
The most useful one for everyday river fishing.
Make an ordinary forward cast, and as the line is unrolling, wiggle the rod tip briskly from side to side. The line lands in a series of S curves along its whole length.
What makes this cast good is that the slack is distributed rather than piled. The current has to straighten each curve in turn before it can begin pulling the fly, and because the curves are spread along the line, the drift extends smoothly instead of ending all at once.
You control the amount by how many wiggles and how big. Two lazy ones for a little slack, half a dozen sharp ones for a lot. It is the most adjustable of these casts, which is why it earns its keep.
It also has the mildest cost. The line is longer than the distance it covers, but it is not in a heap, so a firm sweep of the rod picks it up reasonably well.
Slack Line Casts: An IntroductionThe stop and drop
Also called a bounce or a parachute cast, depending on who is teaching it.
Make a normal forward cast aimed slightly high, and as the loop turns over, drop the rod tip smoothly toward the water. The line, which was travelling forward under tension, loses that tension and falls with waves in it.
It is subtler than a pile cast and more controllable than an S cast, and it has the advantage of landing the fly accurately, because the aiming has already happened before the slack is introduced. Good for a fish you can see, at moderate range, where you need a few feet of free drift and you also need the fly to arrive in a specific spot.
Feeding line, which extends any of them
Once the drift is under way, none of these casts have to be the end of it.
If you keep the rod tip low and pointed down the line, you can shake or strip line out through the guides as the fly travels, and the current takes it. Done well, a drift that would have ended in six feet continues for twenty or thirty.
The technique is a gentle side-to-side waggle of the rod tip while holding a loop of loose line, letting the current pull it out. It looks like nothing and it is the single most effective way to extend a downstream presentation.
The limit is the same as always. Every foot you feed is another foot between you and the hook.
Getting the slack back out
This is the half that separates people who can fish slack from people who make pretty casts and catch nothing.
Keep the rod tip low and follow the drift with it. As the fly comes back toward you, gather line so that you always have contact within a reasonable distance. As it passes and moves away, feed if you want the drift to continue, or start recovering if you do not.
When a fish takes on a slack line, resist the reflex to strike upward. Lifting the rod tip pulls the slack into the air and does very little to the fly. A long low sweep of the rod to the side, back and downstream, takes the slack out along the surface and comes tight to the hook far more efficiently.
And with a heavily slacked downstream drift, deliberately hesitate. A fish that has eaten a dry fly going away from you will hook itself against the tension you eventually apply, and striking instantly usually just removes the fly from its mouth before it has closed.
The tuck cast belongs to a different problem
Worth separating out, because it looks like a slack line cast and is not one.
A tuck cast drives the fly down hard so it enters the water ahead of and below the leader, and it happens to leave slack behind it. But its purpose is depth, not drift protection. You use it to get a weighted nymph to the bottom fast in a short piece of water, which is a completely different objective from keeping a dry fly floating naturally.
The distinction matters because the two want opposite things afterward. A slack-line dry fly presentation wants you to leave the slack alone and let it feed out. A tuck cast wants you to remove the slack immediately and get into contact, because the whole point is feeling what a nymph is doing near the bottom.
We treat it separately for exactly that reason.
Slack on a still water
Everything above assumes current. Lakes and ponds change the problem and most anglers never adjust.
There is no drag in still water in the river sense, because nothing is pulling your line anywhere. What there is instead is wind, which pushes surface line and drags a fly just as effectively, and a subsurface presentation where slack simply means you cannot feel a take.
So the rule inverts. On still water you generally want less slack rather than more: a straight line to the fly, so a lift or a strip reaches it immediately, and so a take registers as something you feel rather than something you hope you saw.
The exception is a dry fly to a cruising fish, where a little slack lets the fly sit dead on the surface rather than being tethered to a line that the wind is bowing. A stop and drop is the right cast for that, and it is about the only slack-line delivery that earns a place on a lake.
Which one to use
The decision is mostly about where the drag will come from.
If the fast water is between you and the fish, use a reach cast toward it and add an S cast if the reach alone is not enough. That is the everyday combination on a trout river.
If you are fishing directly downstream, use a pile cast, then feed line. There is no reaching your way out of a downstream drift.
If you can see the fish and need both accuracy and a few feet of free float, use a stop and drop.
And if you need contact more than drift, use none of them. Nymphing with a tight line, swinging a wet fly and stripping a streamer all want a straight line, because in those the current moving your fly is the point rather than the problem.
How to tell whether you have it right
The feedback loop here is unusually good if you know what to watch, and unusually easy to miss if you do not.
Watch the fly, not the line. A dry fly that is drifting properly sits still relative to the bubbles and foam around it. If it is creeping ahead of them, or sliding across them, or leaving a small wake, drag has started, and you can see it well before a fish reacts to it.
Foam is the cheapest drift indicator in existence. Pick a bubble beside your fly at the start of the drift and watch whether the two stay together. When they separate, that is the moment your drift ended, and the number of seconds it lasted tells you exactly how much more slack the next cast needs.
The second tell is the refusal. A fish that rises to the fly and turns away at the last instant has usually seen something wrong with the way it was moving. One refusal is chance; three from the same fish means the drift is the problem rather than the pattern, and most anglers respond by changing flies, which fixes nothing.
The third is a take you missed. If the fish ate and you could not come tight, you had more slack than you could recover. That is useful information too, and it points the other way: less next time, or a lower and earlier sweep.
Where this matters most
Slow, clear, hard-fished water, which is where the biggest brown trout usually live and where they have seen everything. Spring creeks and tailwaters are the extreme case: fish holding in glassy water with an unobstructed view, refusing anything that moves half an inch out of line with the current.
Any dry fly presentation to a rising fish, which is often a rainbow trout sitting on a seam with faster water between you and it.
And any situation where the geometry gives you no good angle. When you cannot get downstream of the fish, cannot cross, and cannot get closer, slack is what is left.
The gear
A leader long enough to hold slack of its own. A short stiff leader lands straight regardless of what you do with the rod, which defeats every cast here.
Supple tippet, and enough of it. Two or three feet of fine tippet is where most of the useful micro-slack lives, and it is the cheapest presentation upgrade available.
A floating line you can see. Every one of these casts is judged by looking at what the line did on the water, and a drab line in flat light teaches you nothing.
A rod with a responsive tip, because the S cast and the stop and drop are both tip movements. Very stiff tips make small deliberate wiggles into big clumsy ones.
Fly floatant that actually works, since a slack-line presentation is wasted on a fly that is sitting half drowned.
Polarized glasses, again, for reading current and for watching your fly through a drift you cannot feel.
And a willingness to fish downstream. Most anglers work upstream by habit, which avoids the drag problem rather than solving it, and it means they rarely practice the casts that would open up the water they are walking past.
Before the trip
Flow decides how much slack a given piece of water demands, and it changes through the season; reading a river gauge covers checking before you drive. And where there is no room behind you for any of these deliveries, the roll cast still accepts a high aiming point and will give you a surprising amount of slack for free.
The short version
Slack buys drift and costs contact, and the skill is putting in exactly as much as the water demands. Pile casts concentrate slack near the fly for downstream presentations. S casts spread it along the line and are the most adjustable. Stop and drop gives you slack without losing accuracy. Feeding line extends any of them indefinitely.
Get the slack back out with a low sweeping set rather than a lift, and hesitate on a downstream take.
And remember that the alternative to all of it is standing somewhere better.
