Before you spearfish — this comes first
- Get proper instruction before you spearfish. A recognised freediving or spearfishing course teaches the things that actually kill people in this sport, and reading about them is not the same as being taught them.
- Dive with a buddy, and dive one up, one down — one diver in the water, one on the surface watching them, every dive. A breath-hold blackout is silent and gives no warning; a watching buddy is the difference between an incident and a fatality.
- Stay inside your own training and experience. Depth and breath-hold times are personal, they change day to day, and nobody else's numbers apply to you.
- Understand the conditions before you enter the water: visibility, current, swell, tide, boat traffic and your exit. Conditions decide whether a dive is reasonable far more often than skill does.
- Use equipment you have been shown how to use, check it before every session, and be visible — a marked float and line are how boat traffic knows you are there.
- Never extend a dive for a fish. No catch is worth pushing a breath-hold, and the urge to take one more second is exactly what a blackout feels like from the inside — which is to say, like nothing at all.
Tide and current for divers
Explainer · Last reviewed 2026-08-19
Tide decides where food is delivered and whether a diver can get back — and the second consideration outranks the first every time.
Safety
Moving water and currents — Can cause serious injury or death
A diver absorbed in hunting drifts downstream or is caught by a strengthening tidal stream, and cannot swim back to the exit while cold and tired.
What reduces it: Planning so drift runs towards the exit, knowing the state of tide and when it turns, testing progress against the flow before committing, and treating slack water as a window with a known end.
For a rod angler the tide is mostly a question about feeding. For a diver it is also a question about whether the swim home is possible.
WHAT TIDE DOES TO THE FISHING. Moving water carries food, concentrates it on structure, and triggers feeding. Fish position themselves relative to flow, generally facing into it and holding behind whatever breaks it — a rock, a reef edge, a gully mouth. That is predictable and it is the most useful piece of current intelligence there is.
WHAT TIDE DOES TO THE DIVER. Current is a physical constraint on a swimming person, and the threshold at which it becomes unmanageable is far lower than most people expect. A current a diver can swim against for two minutes is not a current they can swim against for twenty, and the difference between those two matters if the exit is upstream.
SLACK WATER — the period around the turn when flow is minimal — is when many marks are diveable at all. It is also short, and it ends on a schedule that is knowable in advance and forgotten in the water.
SPRINGS AND NEAPS change the whole picture. A mark that works comfortably on a neap tide can be undiveable on a spring, and the tidal range in some places — the Solway, the Severn, parts of Brittany, the Bay of Fundy — is large enough that the ground itself is a different place at each end of the cycle.
The rule that keeps divers out of trouble
Plan the dive so that any drift is TOWARDS the exit, not away from it.
A diver who enters upstream and works down has a swim back against current at the end, when they are cold and tired. A diver who enters downstream and works up has the current helping them home. That single decision is worth more than any amount of fitness.
The second rule: know the state of tide when you get in and when it turns. A current that was manageable at slack water will be at its strongest two or three hours later, and a diver absorbed in hunting will not notice the change until they try to go somewhere.
And the third: if you cannot make progress against the current on the surface, you cannot rely on making it underwater either. Testing that at the entry — swimming a short distance against the flow before committing — is a cheap and reliable check.
Where current is genuinely strong, a float line becomes a liability as well as an asset: it drags, and the drag is proportional to flow.
Authoritative guidance
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance on planning dives around tidal streams, drift direction and exit points.States this directlyCitation checked — the work exists and is described correctly
- NOAA Ocean Service tides and water levels educational tutorial — National Oceanic and Atmospheric Administration, United States (Government fisheries body)Relied on for: Tidal mechanics including the relationship between lunar phase, spring and neap ranges, and tidal stream timing.States this directlyPassage read and verified
Where tidal thinking transfers and where it does not
In the MEDITERRANEAN, tidal range is very small and tide is largely irrelevant to a diver's planning. Current there is driven by wind and by local topography instead, which means a Mediterranean diver's instincts about current do not transfer north.
In THE UK, IRELAND, ATLANTIC EUROPE AND MUCH OF NORTH AMERICA the tidal range is substantial, tidal streams are the dominant current, and tide tables are essential planning equipment rather than an interest.
In parts of AUSTRALIA, NEW ZEALAND AND THE INDO-PACIFIC the picture is mixed: modest tidal range in places, and strong topographically driven currents around passes and channels that are effectively permanent.
The transferable part is the reasoning — flow concentrates food, structure breaks flow, and the exit must be reachable — rather than any specific expectation about how much water will move.
Where to go next
Where it matters
- Shore divingA current manageable for two minutes is not one manageable for twenty, and the exit may be upstream.
- SpearfishingTidal streams decide the ground a breath-hold diver can work and the leg they can return on.
What these connections rest on (2)
Authoritative guidance — 2 connections
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Shore diving
Where the constraint is felt.
- NOAA Ocean Service tides and water levels educational tutorial — National Oceanic and Atmospheric Administration, United States (Government fisheries body)Relied on for: Tidal mechanics including lunar phase, spring and neap ranges, and tidal stream timing.States this directlyPassage read and verified
Spearfishing
A membership assertion rather than a topical one: this record teaches the discipline or its equipment, so the discipline's mandatory safety posture applies to it.
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Breath-hold spearfishing as a defined discipline with its own technical, equipment and safety standards, set out by the international underwater federation.States this directlyCitation checked — the work exists and is described correctly
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: That the safety requirements of breath-hold diving apply across the discipline rather than to particular equipment or techniques within it.States this directlyPassage read and verified
Related reading
- Planning a dive sessionState of tide, when it turns, and planning so that any drift carries the diver towards the exit rather than away from it.
- Spearfishing in UK and Irish watersAmong the most tidally energetic coasts anywhere, where slack water is frequently the entire dive window.
- Why a lead will not hold bottomCurrent acts on everything in the water, and the length of line in the flow decides how much of it there is to act on.
What these connections rest on (3)
Authoritative guidance — 2 connections
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Planning a dive session
The condition the plan is mostly built around.
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance on planning, conditions assessment, buddy protocol, entanglement and equipment handling.States this directlyCitation checked — the work exists and is described correctly
Spearfishing in UK and Irish waters
The condition that decides whether there is any diving at all on a given day.
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance on conditions assessment, buddy separation and entanglement.States this directlyCitation checked — the work exists and is described correctly
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.
Why a lead will not hold bottom
The mechanism behind the diagnosis.
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Terminal tackle behaviour, line drag in flow, bait presentation and rig geometry.States this directlyCitation checked — the work exists and is described correctly
- Pike and the Pike Angler — Stanley Paul, 1981 (Specialist angling publication)Relied on for: Rig and terminal-tackle mechanics described independently of the sea-angling tradition.States this directlyCitation checked — the work exists and is described correctly
How this compares
- Reading the tideTide decides where food is delivered and whether a diver can get back, and the second outranks the first.
- Reading underwater conditionsPlan so that drift runs towards the exit rather than away from it.
- Slack water, and why it is differentFor anybody in the water rather than beside it, slack is the safety window as well as the working one — the period when a race is crossable and a diver can hold position.
What these connections rest on (3)
Authoritative guidance — 2 connections
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Reading the tide
The tidal science and the diver's version of it.
- NOAA Ocean Service tides and water levels educational tutorial — National Oceanic and Atmospheric Administration, United States (Government fisheries body)Relied on for: Tidal mechanics including lunar phase, spring and neap ranges, and tidal stream timing.States this directlyPassage read and verified
Reading underwater conditions
The rule that keeps divers out of trouble.
- NOAA Ocean Service tides and water levels educational tutorial — National Oceanic and Atmospheric Administration, United States (Government fisheries body)Relied on for: Tidal mechanics including lunar phase, spring and neap ranges, and tidal stream timing.States this directlyPassage read and verified
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.
Slack water, and why it is different
Two conditions records a reader will weigh against one another, joined where the contrast is what makes either usable.
- Sea Angler — Bauer Media (Specialist angling publication)Relied on for: Contemporary UK sea angling practice as reported by practitioners, including tidal timing and shore conditions.States this directlyCitation checked — the work exists and is described correctly
- NOAA Ocean Service tides and water levels educational tutorial — National Oceanic and Atmospheric Administration, United States (Government fisheries body)Relied on for: Public education on tidal generation, tidal streams and the relationship between water level and flow.States this directlyPassage read and verified
Sources for this page
- NOAA Ocean Service tides and water levels educational tutorial — National Oceanic and Atmospheric Administration, United States (Government fisheries body)Relied on for: Tidal mechanics, ranges and stream behaviour.States this directlyPassage read and verified
How FishingHQ labels evidence is explained in the evidence policy.