Floating, sinking and intermediate fly lines
Explainer · Last reviewed 2026-08-14
Density decides depth, and depth decides whether the fly is where the fish are. It is the single most consequential line choice and the one beginners change last.
A fly line's density is what decides where in the water column the fly fishes, and getting it wrong is a more complete failure than getting the fly wrong.
FLOATING LINES sit on the surface. They are the default, they are the easiest to lift and recast, they are essential for dry flies and surface work, and with a weighted fly and a long leader they will fish deeper than most beginners expect. Everything visible happens on a floating line.
INTERMEDIATE LINES sink very slowly — a few centimetres a second — and they are the most under-used line in fly fishing. They fish just under the surface, they stay under the disturbance of a chop instead of being lifted and dragged by it, and on a windy coast or an exposed stillwater they hold a straight line to the fly where a floater cannot. For coastal fly fishing they are frequently the correct first choice rather than a specialist option.
SINKING LINES are rated by how fast they sink, and the rate is the useful number. A faster sinker is not better; it is for deeper or faster water. The technique is to count the line down and then repeat what worked, which turns depth from a guess into something reproducible.
SINK TIPS put a short sinking section at the front of a floating line. They get a fly down while keeping most of the line liftable, which makes them a practical compromise on rivers and from a boat.
THE PRINCIPLE UNDERNEATH ALL OF IT is that fish feed at a depth determined by temperature, light, oxygen and where the food is, and that depth changes through the day and the season. A reader who owns one floating line is fishing one narrow band of water and attributing the result to fly choice.
AND THE RETRIEVE INTERACTS WITH THE DENSITY. A fast retrieve lifts a sinking line towards the surface and a slow one lets it keep sinking, so the same line fishes at different depths depending on how it is worked — which is a feature to be used deliberately rather than an inconsistency to be worried about.
Density is how a fly line controls depth, and why the sea needs it more
A fly weighs almost nothing, so in fly fishing the LINE is the thing that has mass and therefore the thing that decides where the fly ends up.
A FLOATING LINE keeps everything at the surface and gives the most control: it can be mended, lifted and repositioned, and it makes the take visible. Its limitation is that it holds the fly up. A weighted fly on a floating line sinks on the pause and then RISES through the whole retrieve, which is either exactly what you want or exactly what you do not.
AN INTERMEDIATE SINKS SLOWLY AND MORE OR LESS STRAIGHT. It gets under surface chop and wind drift and holds a fly at a shallow constant depth through a retrieve, which is the single most useful property on an open coast — where surface wind pushes a floating line and a bag forms between rod and fly. For a great deal of coastal fly fishing an intermediate is the default rather than a specialist choice.
A SINKING LINE IS RATED BY SINK RATE, and the rating is what makes depth controllable rather than approximate: a line quoted at a given inches-per-second, counted down for a known number of seconds, puts a fly at a repeatable depth. Count down, retrieve, and if nothing happens count down further. That is the whole method, and it is what turns depth into a variable you can search rather than a hope.
DENSITY-COMPENSATED LINES sink with the tip leading rather than bellying in the middle, which keeps a straight line between hand and fly. The practical consequence is contact: a bellied sinking line registers a take late or not at all.
SHOOTING HEADS put the mass in a short front section with thin running line behind it, which buys distance and turnover in wind at the cost of delicacy — and delicacy is worth less on a coast than it is on a chalk stream.
SO THE HONEST DECISION LOGIC. Surface activity, calm, shallow: floating. Open coast, chop, wind, fish in the top couple of metres: intermediate. Deep water, current, fish holding down, or a need to search depths systematically: a rated sinker, counted down. And nothing here is a ranking — a line is a tool for a depth, and the reason to own several is that the fish choose the depth.
Practitioner consensus
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Fly-fishing practice from a practitioner tradition: line control, presentation, depth management and the reading of water.States this directlyCitation checked — the work exists and is described correctly
- Sea Angler — Bauer Media (Specialist angling publication)Relied on for: Contemporary UK sea angling practice as reported by practitioners: ground, tackle, presentation and seasonal timing.States this directlyCitation checked — the work exists and is described correctly
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: Widely restated descriptions of technique, tackle convention and regional practice, recorded as consensus rather than as scholarship.Background and mechanism onlyCitation checked — the work exists and is described correctly
Where to go next
Fish this applies to
What these connections rest on (1)
Practitioner consensus — 1 connection
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Rainbow trout
A fish or a water joined to the fly-fishing mechanism it is a worked example of, written only where the subject's own behaviour or physical character is what the record explains. The direction is the one the predicate table allows and the one the graph already uses 176 times, and it is also the semantically correct one: the mechanism explains the fish, not the reverse.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Stillwater fly practice: line density and depth, leader construction, fly selection against the food present, and the behaviour of stocked and wild trout in still water.States this directlyCitation checked — the work exists and is described correctly
- Trout & Salmon — Bauer Media (Specialist angling publication)Relied on for: Long-running published description of British game angling practice: river and stillwater trout, grayling and salmon fishing, and the presentation each demands.States this directlyCitation checked — the work exists and is described correctly
- Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: Life history, feeding biology, habitat requirement and seasonal behaviour of the freshwater fishes of the British Isles.States this directlyCitation checked — the work exists and is described correctly
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Recorded environment, depth range, feeding biology and distribution of the species named.States this directlyPassage read and verified
Where it matters
- Saltwater fly fishingDepth in salt is controlled by line density rather than by fly weight, and the counted-down sinker is what turns depth into a variable you can search.
- Stillwater fly fishingStillwater fly fishing is where counting a sinking line down turns depth from a guess into something reproducible, and the method depends on the distinction.
What these connections rest on (2)
Practitioner consensus — 2 connections
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Saltwater fly fishing
An explainer carrying a mechanism the record depends on.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Fly-fishing practice from a practitioner tradition: line control, depth management, retrieve and the reading of water.States this directlyCitation checked — the work exists and is described correctly
- Sea Angler — Bauer Media (Specialist angling publication)Relied on for: Contemporary UK sea angling practice as reported by practitioners: ground, tackle, presentation and seasonal timing.States this directlyCitation checked — the work exists and is described correctly
Stillwater fly fishing
A mechanism edge between a record and the explanation beneath it. Fly tackle and technique rest on established practitioner craft rather than on experiment, and the support level says so rather than borrowing an authority the subject does not have.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Stillwater fly fishing technique, including line choice, depth control, retrieve and the imitation of stillwater food forms.States this directlyCitation checked — the work exists and is described correctly
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comprehensive freshwater angling practice including fly tackle, casting, presentation and the reasoning behind terminal tackle choices.States this directlyCitation checked — the work exists and is described correctly
Gear this affects
What these connections rest on (1)
Practitioner consensus — 1 connection
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Fly lines
A mechanism edge between a record and the explanation beneath it. Fly tackle and technique rest on established practitioner craft rather than on experiment, and the support level says so rather than borrowing an authority the subject does not have.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Stillwater fly fishing technique, including line choice, depth control, retrieve and the imitation of stillwater food forms.States this directlyCitation checked — the work exists and is described correctly
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comprehensive freshwater angling practice including fly tackle, casting, presentation and the reasoning behind terminal tackle choices.States this directlyCitation checked — the work exists and is described correctly
Water and ground
- Lowland stillwatersThe gentler case, and the one where an intermediate line earns its keep. Shallow enough that a fast sinker is unusable and often too broken by wind for a floater to fish cleanly, which is precisely the gap the intermediate density fills.
- ReservoirsThe water that makes the argument physical. A deep artificial stillwater stratifies in summer, draws down through the season, and holds fish at a depth that changes through the day — so a single line fishes one narrow band of a water that has many.
What these connections rest on (2)
Practitioner consensus — 2 connections
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Lowland stillwaters
A fish or a water joined to the fly-fishing mechanism it is a worked example of, written only where the subject's own behaviour or physical character is what the record explains. The direction is the one the predicate table allows and the one the graph already uses 176 times, and it is also the semantically correct one: the mechanism explains the fish, not the reverse.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Stillwater fly practice: line density and depth, leader construction, fly selection against the food present, and the behaviour of stocked and wild trout in still water.States this directlyCitation checked — the work exists and is described correctly
- Trout & Salmon — Bauer Media (Specialist angling publication)Relied on for: Long-running published description of British game angling practice: river and stillwater trout, grayling and salmon fishing, and the presentation each demands.States this directlyCitation checked — the work exists and is described correctly
Reservoirs
A fish or a water joined to the fly-fishing mechanism it is a worked example of, written only where the subject's own behaviour or physical character is what the record explains. The direction is the one the predicate table allows and the one the graph already uses 176 times, and it is also the semantically correct one: the mechanism explains the fish, not the reverse.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Stillwater fly practice: line density and depth, leader construction, fly selection against the food present, and the behaviour of stocked and wild trout in still water.States this directlyCitation checked — the work exists and is described correctly
- Trout & Salmon — Bauer Media (Specialist angling publication)Relied on for: Long-running published description of British game angling practice: river and stillwater trout, grayling and salmon fishing, and the presentation each demands.States this directlyCitation checked — the work exists and is described correctly
How this compares
- Fly fishing for pollack over rough ground and kelpCounting a sinking line down and repeating the count that worked is the whole method here, and it is the same discipline stillwater fly fishers use.
- Fly line weights, tapers and what they doMass and density are the two independent properties of a fly line, and choosing one without the other is how anglers end up with the right weight at the wrong depth.
- Presentation and dragDepth and drag are the two ways a fly is presented wrongly, and they are usually diagnosed as fly-choice problems instead.
- Saltwater fly fishing: what changesLine density is the choice that changes most on the coast, where an intermediate is frequently the correct first line rather than a specialist option.
What these connections rest on (4)
Practitioner consensus — 4 connections
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Fly fishing for pollack over rough ground and kelp
Two records a reader would reasonably weigh against one another, joined where the comparison teaches something about both.
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comprehensive angling practice including fly tackle, casting, presentation and the reasoning behind terminal tackle choices.States this directlyCitation checked — the work exists and is described correctly
- Trout & Salmon — Bauer Media (Specialist angling publication)Relied on for: Contemporary game and fly angling practice as reported and restated by practitioners, including tackle convention and technique.Background and mechanism onlyCitation checked — the work exists and is described correctly
Fly line weights, tapers and what they do
Two records a reader would reasonably weigh against one another, joined where the comparison teaches something about both. A navigation claim rather than a claim about the world.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Stillwater fly fishing technique, including line choice, depth control, retrieve and the imitation of stillwater food forms.States this directlyCitation checked — the work exists and is described correctly
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comprehensive freshwater angling practice including fly tackle, casting, presentation and the reasoning behind terminal tackle choices.States this directlyCitation checked — the work exists and is described correctly
Presentation and drag
Two records a reader would reasonably weigh against one another, joined where the comparison teaches something about both. A navigation claim rather than a claim about the world.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Stillwater fly fishing technique, including line choice, depth control, retrieve and the imitation of stillwater food forms.States this directlyCitation checked — the work exists and is described correctly
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comprehensive freshwater angling practice including fly tackle, casting, presentation and the reasoning behind terminal tackle choices.States this directlyCitation checked — the work exists and is described correctly
Saltwater fly fishing: what changes
Two records a reader would reasonably weigh against one another, joined where the comparison teaches something about both. A navigation claim rather than a claim about the world.
- Trout & Salmon — Bauer Media (Specialist angling publication)Relied on for: Contemporary game and fly angling practice as reported and restated by practitioners, including tackle convention and technique.Background and mechanism onlyCitation checked — the work exists and is described correctly
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: Widely restated angling practice and belief, recorded as practitioner consensus rather than as tested fact.Background and mechanism onlyCitation checked — the work exists and is described correctly
Sources for this page
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Stillwater fly fishing technique, including line choice, depth control, retrieve and the imitation of stillwater food forms.States this directlyCitation checked — the work exists and is described correctly
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comprehensive freshwater angling practice including fly fishing tackle, casting, presentation and the reasoning behind terminal tackle choices.States this directlyCitation checked — the work exists and is described correctly
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: Widely restated angling practice and belief, recorded as practitioner consensus rather than as tested fact.Background and mechanism onlyCitation checked — the work exists and is described correctly
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