spearo sea-state engine: consensus of up to 6 models + satellite clarity (ZSD) + buoy-bias checks
Freshness
Re-read every hour, per coast
Compiled by the spearo sea-state engine · How it works →
The verdict comes from seven water factors and hard safety gates — not ten tabs. Go or stay.
How we score the water
Our own model
Our own forecast engine — not a third-party widget. It weighs these water factors into one go-or-stay verdict for this coast; the 0–10 dial is that verdict, read out as a number.
01
Swell & wave memory
Height, period and direction of the swell, plus the wake of recent storms — an old storm still stirs the water, and the engine remembers.
02
Wind & gusts
Speed and gusts, hour by hour — wind speed and an onshore push chop the surface and cut visibility.
03
Tide phase
Timing and range of the tide, calibrated per coast — big spring tides pull the verdict toward caution.
04
Water temperature
Sea-surface temperature — sharply cold water vetoes a green verdict.
05
Currents & outflow
Direction and drift of the current — it pushes you, and it drags turbid coastal water across where you dive.
06
Rain runoff & air clarity
Rain muddies the water inshore through land runoff, while fog and haze cut visibility at the surface.
07
Coast shape & exposure
How the coast faces the swell — a sheltered cove keeps the water clean; an exposed, head-on point takes a penalty.
Safety gates
Thunderstorm forecast — an instant red, no exceptions.
An official warning (MeteoAlarm / IPMA) — yellow, or red for the higher ranks.
Missing input data — a would-be green is capped to yellow rather than overstated.
Strong disagreement between forecast models — a green day is pulled back to yellow.
Night hours — where night spearfishing is banned by law the window is forced red; where it is legal (Australia outside NSW, New Zealand, South Africa) it is capped at yellow, never green.
It all folds into a single 0–10 score and one verdict: go or stay.
A forecast, not a guarantee — the sea has the last word.
Where to get in, where to hunt
Entry points with coordinates
Seabed relief — promising ground
This verdict — in your pocket. Open the app for the week's window.
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0 m
Surface
Wind, wave and the swell windows — when to go and the best hours.
spearo.app
no dataupdated 03:34
Arenys de Mar — solo, off the rocks
BEST WINDOW
best weather window · solo, stay careful, run the checklist · calm conditions: swell, wind and visibility all normal
What's missing? Tell us what you'd like to see — new spots, species, data or features. We read everything.
Your best window — with you. Forecast in your pocket.
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−10 m
The water column
Visibility and what drives it — post-storm clearing, river plume, temperature and the thermocline.
What it is
A marine instrument, go / no-go for solo hunting.
spearo.app folds wind, wave, swell period, visibility, tides, water temperature and risk into a single verdict — go to the spot or not. It computes 7 days ahead from open marine models (Open-Meteo, IPMA), with no sign-up and no accounts. Built for solo spearfishing off the rocks, where any mistake costs dearly.
Now live: 3016 spots across 406 stretches of coast — mainland Portugal, Madeira and the Azores.
Relief and bottom type, tides, and the depths of each spot.
On the rock
The forecast is the plan. The call is on the rock.
The models set the window. Whether you go in is read only at the water: count the sets, watch the surge on the entry. If in doubt, you don't get in.
Entry points
No verified spots here yet
The forecast is calculated for the shore next to the town.
We publish no entry here, and that is not a hole in the catalogue. The Maresme between Mataró and Calella is nourished sand between groynes, and the only relief is the breakwaters of Arenys harbour — the working fishing port of this coast, with the trawler fleet coming through the mouth and a full marina. The bottom in front is sand a long way out, the water goes brown with every levante, and the whole strip is bathing water with swimmers into October. The real rock is at both ends: north-east the Costa Brava (the nearest no-take ring, Ses Negres, is over 68 km away) and south-west the Garraf massif, which in this atlas is called Sitges. Go there, not into the harbour mouth.
One morning glance — and you know.
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≈
Surfacing
Cameras, map and reference — to hand as you come up.
Sin prohibición estatal de captura (NO está en el Catálogo Español, RD 139/2011). Cataluña: 50 cm, máx. 2 ejemplares/día — Resolució ARP/3310/2025.
common octopus
Octopus vulgaris · Mediterranean · 1 kg
Talla por PESO: mín. 1 kg (RD 560/1995, todos los anexos). No coger hembras con huevos. Cataluña: veda del pulpo de roca aprox. jul–sep, por zonas — Resolució ARP/3310/2025.
Law
✓Spearfishing licence mandatory; the AUTONOMOUS COMMUNITY issues it (not the State) and it is valid in the exterior waters of the whole coast. Free-diving only — scuba is banned (, art. 3).
✓Spearfishing catch may not be sold or traded — it is non-commercial fishing ().
✓Night prohibited: spearfishing only in daylight (sunset to sunrise not allowed) — , art. 16.d.
✓Marker buoy MANDATORY: mark your position with a clearly visible buoy and stay within 25 m of it — , art. 15.
✓Never keep the speargun loaded out of the water — , art. 16.a.
✓Keep at least 300 m from professional fishing vessels that are working — , art. 12.b.
✓The state act (, art. 16) bans, for spearfishing: a loaded gun out of the water; explosive/electric points and lamps (hand torches excepted); underwater scooters; night — from sunset to sunrise. Plus art. 12 b), d), e): 300 m from professional fishing vessels, light as an attractant, poisons/explosives. A ban in a PARTICULAR reserve, port or beach comes from that place's OWN instrument (the reserve's order, the autonomous community's rules, the port authority) — see the no-take zones on the map and your community's rules.
✓Min. sizes by ( + + EU 2019/1241): sea bass 42 cm (rec.) / 36 cm / 25 cm Mediterranean / 22 cm Canaries; gilthead bream 20 cm and white seabream 23 cm in the Mediterranean (EU 2019/1241); grouper 45 cm. See your zone's species card.
✓Only species in Annex I of may be taken; keeping, landing or transporting undersized specimens is prohibited.
✓The licence needs a medical fitness certificate for free-diving and civil-liability insurance (or a federative licence, which includes it). Mandatory in the Basque Country/Murcia/Asturias/Galicia; the federative licence covers it in Galicia/Balearics/Cantabria; the Canaries and Andalusia do NOT require it for the individual licence (a responsible health declaration). Minimum age generally 16 (14 in Andalusia).
Safety protocol
Sets: watch the wave trains ≥15 min before entering; Hmax ≈ 2×Hs, the wash can run 50 m past the foam line. A lull >10 min with period >12 s = a big set «overdue», do NOT enter; enter right after a full set passes and re-check at minute 30.
Exit FIRST: find your exit AND a backup before entering. On a rocky/boulder shore a 0.5 m rise in swell can make the exit impossible — getting pinned/unable to climb out is the main killer.
Headland rip: prominent points often have a permanent topographic rip regardless of the model — locate it, enter/exit on the windward side, never swim against it.
Cold: wetsuit per the SST chip; the first shiver = a metabolic surge and a drop in breath-hold → get out at the first steady shiver. Cap the session at 45–60 min below 15 °C.
Solo discipline: buoy up; tell someone the spot and exit time; conservative breath-hold (never push it in cold/murky/surfy water); visibility <3 m — don't enter.
Afternoon wind: on many coasts the wind builds from midday — plan to be out of the water by midday; the chop builds — get out.
UV 11:00–15:00 (UVI ≥6): sunscreen and cover up on the surface interval.
Solo is a fundamental risk (hypoxic blackout with no buddy). Any doubt = No-go.
FAQ — spearfishing in Arenys de Mar
Where can I spearfish in Arenys de Mar?
No marks are published for Arenys de Mar, by design. Check today's forecast above and pick a calm-sea day, always with a marker buoy.
When is the best season in Arenys de Mar?
Long season (May–October), with summer going glassy. Tide barely matters — follow the solunar and the thermocline; there are posidonia meadows and, at peak summer, plenty of boats and swimmers.
How cold is the water in Arenys de Mar?
Mediterranean: ~13 °C in winter to ~25 °C in summer. A 3 mm suit in high summer, 5 mm in spring and autumn — but the thermocline can leave the water much colder at depth.
Is Arenys de Mar good for a beginner?
Accessible: generally calm sea, clear water and little current — good for building water time on small-sea days. Mind the boat traffic in summer; always use the buoy.
Do I need a licence in Arenys de Mar?
Yes — in Arenys de Mar you need a recreational sea-fishing licence (issued by the autonomous community); breath-hold only (no scuba), with a marker buoy and no night diving. See the guide.
✓There is no fixed national catch cap (, art. 5 delegates it to the communities); the standard is 5 kg/person/day, with 1 specimen allowed not to count (Canaries — Decreto 182/2004, art. 38.3; Murcia; Galicia; Basque Country). Protected species have per-piece quotas.
✓Only a harpoon is allowed — hand-held or mechanically propelled, with one or several points (, art. 14.1). Carrying spearfishing gear and underwater breathing equipment aboard AT THE SAME TIME is prohibited (art. 14.2) — an offence in itself, even if you dived on a breath hold.
✓Spain is not one jurisdiction. The licence is issued by a coastal autonomous community, and you must comply with the rules of the administration on whose littoral you are in the water: «debiendo cumplir la normativa establecida por la administración en cuyo litoral se realice la actividad» (, art. 13). Interior waters — inside the straight baselines: bays, coves, rías, the whole coastal strip — are the community's competence; exterior waters are the State's. So the age, the days of the week, the distances and the are found in your community's act, not in the state one.
✓Catalonia: the «Llicència de pesca recreativa subaquàtica» (recreational spearfishing) is issued by the Generalitat de Catalunya — applied for at tramits.gencat.cat.
✓Bans: Illes Medes, Ses Negres (Begur), parts of Cap de Creus — spearfishing banned (see zones).
✓Catalonia (Decret 109/1995): the daily cap per licence is 10 kg of fish, 5 kg of cephalopods and 150 sea urchins (art. 25.1); the excess weight of one big specimen does not count (art. 25.2), and for tuna and swordfish there are no kilos at all — the cap is 2 pieces a day (art. 25.3). Sunrise to sunset only (art. 15), on a breath hold, with a hand spear or a mechanically propelled gun that may be loaded ONLY under water (art. 16). Keep 100 m from set gear, marine farms, anglers' rods and professional vessels, and at least 250 m from bathing zones measured along the shore (art. 17); lamps, torches, powder- or gas-propelled guns and explosive points are banned (art. 18); a surface buoy is mandatory (art. 19). Only fish, cephalopods and sea urchins may be taken (art. 24.1), and the triton (Charonia lampa — así lo imprime el decreto), the fan mussel (Pinna nobilis) and the date mussel (Lithophaga lithophaga) may not be collected at all (art. 24.2).
Spain