The rocks are already written down. They are just written down where nobody looks.
In August 2026 a chartered yacht hit a reef north of Frikes, Ithaca, running
both Navionics and Orca. Neither showed it. The owners said everyone local knows
about that rock — and they were right, which is the problem.
It is called Agriógatos. Its position has been printed in a free cruising guide
for years, 3.6 m from where a stranger dropped a Google Maps pin reading
“Attention reef”.
Then the same shape appeared 2,000 km away. Las Erretas, off Hendaye — a reef
that has taken boats, known to every local, carrying four names in three languages:
Erretas, Les Couteaux du Diable, Les Briquets. Google Maps labels it. OpenStreetMap has nothing
under any name. No search for it as a hazard returns a position. It surfaced only because a sailor
on a Spanish forum wrote «mucho respeto hay que tenerles» — and the one published
coordinate on earth turned out to be a single line typed by one user in 2019.
Both cases are the same failure, and it is not a survey failure. Every hazard below was compiled
from prose that already existed. No sonar, no satellite, no new data.
Pre-departure hazard brief
Ionian — Lefkas to Kefalonia
Lefkas · Meganisi · Kalamos · Ithaca · Kefalonia
hazards listed
8
with a position
2
conditional
0
The Ionian hazard is a fixed obstruction: it is either encoded on the chart or it is not. Seven entries, compiled in an afternoon from one free cruising site. The first is the reef that started this.
Agriógatos reef
Corroborated
Ithaca — Marmagkas (Agios Nikolaos) bay, N side of the entrance
38°28.937′N20°40.597′E
50 m wide · 241 m offshore
50 m wide reef on the north side of the bay entrance, roughly 250 m offshore and 287 m NNE of the islet. Unmarked: no buoy, no cardinal, nothing on the water to see.
The dashed track stops where the boat did. Reported local practice, unverified. The published guide names the reef and its position and says it lies «in the middle of the northern approach» — but never states the southern approach as the answer. That instruction exists only in local heads.
Avoiding actionEnter the bay passing SOUTH of the islet — there is 235 m of clear water between the islet and the shore. Do NOT pass north of the islet: that route threads the 287 m gap between the islet and the reef, and it is the one boats hit.
Where this came from
Position published in a cruising guide
sailingissues.com derrotero (with coordinates)
Google Maps user POI 'Attention reef' — 3.6 m from the published position
verified grounding, Aug 2026
Local practice reported by the yard owner after the grounding — unverified
Electronic charts — navionics: not shown (skipper report, Aug 2026) · orca: not shown (skipper report, Aug 2026) · openseamap: absent (0 seamark objects within 1 km)
Atherinos reef
Corroborated
Meganisi — Atherinos bay / Cape Elia
38°40.027′N20°47.961′E
Reef connected to Cape Elia, called 'infamous' in English sources. The Greek guide is more specific and adds a second danger the English sources omit: «Προσοχή στους υφάλους βόρεια του κόλπου του Αθερινού και μέσα στον ίδιο κόλπο δεξιά όπως εισέρχεστε» — reefs north of Atherinos bay, and inside the bay itself to starboard as you enter.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionFavour the port side going in — the Greek source puts the inner reef to starboard on entry. Anchor in deep water with a line ashore rather than working close round the cape.
Where this came from
Position published in a cruising guide
sailingissues.com derrotero (with coordinates)
Greek source (Lefkada Slow Guide) — adds the inner reef and which side to favour; absent from every English source
The sandbank and silts at the north end of the canal continuously change shape. Charted depths go stale between surveys. Three groynes marked by yellow buoys.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionFollow the buoyed channel exactly. Do not trust charted soundings here — they describe a seabed that has since moved.
Where this came from
No published position — area-level warning only
sailingissues.com
standard charter briefing item at every Lefkas base
Electronic charts — navionics: charted but stale by design · orca: charted but stale by design
Kalamos port reef
Single source
Kalamos — port approach
no published position
100 m offshore
Reef bearing 045° at 780 m from the harbour light, about 100 m off the coast. A stone awash lies directly east of the port.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionDo not approach Kalamos port from the NE quadrant close in. Come in from seaward and pick up the harbour on a clean bearing.
Where this came from
No published position — area-level warning only
sailingissues.com, cross-referenced to Eagleray, Garmin and C-Map cartography
position derived from published bearing/range — verify before relying on it
Between the SW tip of Skorpios and Spartochori, Meganisi
no published position
Reef in the channel between the south-west tip of Skorpios and Spartochori, on the direct route from Lefkada to Meganisi. The Greek source: «Χρειάζεται ιδιαίτερη προσοχή αυτός ο ύφαλος διότι “αναδύεται” ξαφνικά και το βυθόμετρο δεν βοηθά» — it rises so abruptly that the depth sounder gives you no warning.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionDo not rely on the sounder here; by the time it reads, you are on it. This is a hazard you clear by position, not by instrument. Coming from Lefkada, stand off the south-west corner of Skorpios.
Where this came from
No published position — area-level warning only
Lefkada Slow Guide (Greek) — «το βυθόμετρο δεν βοηθά»
Found only by searching in Greek. Does not appear in any English-language source checked.
No coordinates published — described by its position between two landmarks
Electronic charts — An instrument-failure warning. No chart symbol exists for 'your echo sounder will not save you here'.
Reef off the entrance
Unverified
Arkoudi — anchorage entrance
no published position
Reef extending from the south side of the entrance.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionFavour the north side on the way in.
Gipuzkoa · Lapurdi · Urola bar · Belharra · Les Briquets
hazards listed
13
with a position
6
conditional
8
A second region, both sides of the border, to test whether the pipeline generalises. It does. But the hazard physics are different: most danger here is conditional — a bar flat at half tide and breaking on the ebb, a 16 m shoal that becomes a 15 m wave twice a decade. No chart symbol can carry that. Note also what happens to names at a border.
Belharra-Perdun
CorroboratedConditional
Urrugne — 2.5 km NW of the baie de Saint-Jean-de-Luz
43°24.617′N1°43.133′W
16.0 m over it · 2500 m offshore
Shoal rising to 14–18 m, 2.5 km offshore between Socoa and Hendaye. In big NW swell it raises a breaking wave of 8 to 15 m. It does not break most years at all — before the breakwaters were built it swallowed vessels moored between Bidart and Guéthary.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionThe chart shows 16 m and nothing else, so on 360 days a year this is open water. On the wrong day it is a 15 m breaking wave over your route. Check the swell forecast, not the depth.
Where this came from
Coordinates published by the source
Wikipédia FR — with coordinates and depth range
named as one of the four passes into the bay
Electronic charts — Charted as a depth. Nothing on a chart can express that a 16 m sounding sometimes breaks.
Las Erretas / Les Briquets
CorroboratedConditional
Hendaye → Saint-Jean-de-Luz — off the Corniche basque
43°23.732′N1°44.980′W
3.0 m over it · 1000 m wide · 2000 m offshore
A plateau of long rocky slabs 2 km off Hendaye, depths 3–12 m, several of which «émergent (à basse mer) ou sont justes sous la surface». Spans roughly 1,000 m with multiple rocky heads. Straddles the coastal route Hendaye → Saint-Jean-de-Luz. It has four names — Erretas (ES/EU), Les Couteaux du Diable and Les Briquets (FR) — and no chart or database carries them all.
The dashed track stops where the boat did. Local practice from Spanish forum threads, geometrically verified here but not published in any chart or guide: «si unes una línea entre el faro de Higuer y el de Biarritz y navegas al norte de ello, las evitas.» One transit clears both reefs.
Avoiding actionJoin Cabo Higuer light to the Biarritz light and stay north of that line. It is a visual transit — both lights are in sight — and it clears Las Erretas by 1,449 m and Belharra-Perdun by 1,313 m in one stroke. To enter Saint-Jean-de-Luz you must cross it; do that east of Belharra.
Where this came from
Coordinates published by the source
Transit rule: «si unes una línea entre el faro de Higuer y el de Biarritz y navegas al norte de ello, las evitas» — verified by computation (Briquets 1,449 m inshore of the line, Belharra 1,313 m inshore). Published in no chart or guide found.
masmar derrotero de Euskadi: «Tanto este canal como los pasos que dejan entre si las piedras que emergen de Les Briquets solo son abordables con buen tiempo, sin mar de fondo y POR CONOCEDORES DE LAS MARCAS.» — the guide states that local marks are required, and withholds them.
sea-seek.com publishes the position — but the whole entry is one line typed by one user («azertv») on 7 June 2019: «Attention à cette zone de hauts fonds qui couvre et découvre!» That single seven-year-old edit is the only published position for this reef anywhere.
latabernadelpuerto.com forum — «Y Erretas es un arrecife de bastante respeto… más de uno ya ha quedado allí»
mibaluma.blogspot.com log — marks it as a GPS waypoint in order to clear it
lechasseursousmarin.com — 2 km offshore, 3–12 m, slabs that emerge at low water
Google Maps carries the label «Les Briquets». OpenStreetMap has nothing under any of its four names.
Found by searching sailors' vernacular, not hazard nouns. Position inferred from prose («2 km du littoral») was 702 m wrong before the published coordinate was found.
Electronic charts — The masmar derrotero covers this bank properly — extent, the freu, depths of 3–11 m — and then says the passage is «solo abordable… por conocedores de las marcas». It names the gap in itself: the marks are necessary, and it does not print them.
Roches Noires
CorroboratedConditional
Hendaye — off Pointe Sainte-Anne
43°23.279′N1°44.925′W
Rocks on the inshore side of the freu from Les Briquets; some emerge at low water. Published waypoint at its northern edge: 43º 23,279'N / 001º 44,925'W. The channel between Roches Noires and Les Briquets carries 3–11 m.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionThe freu is passable «con buen tiempo, sin mar de fondo y por conocedores de las marcas». If you do not know the marks, you are not one of those people — go outside Les Briquets.
Where this came from
Published waypoint
masmar derrotero de Euskadi — with waypoint
forms the inshore side of the Briquets channel
Barra de Zumaia
CorroboratedConditional
Zumaia — Urola river bar
no published position
River bar. The Santiago beach sand spit has joined the counter-dike and dries at major low waters. The whole bight is very shallow and the sea builds over it in swell.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionThis is a conditional hazard, not a fixed one. Safe in calm at half tide, breaking and lethal on the ebb in northerly swell. Cross near high water, never on an ebb against swell.
Where this came from
No published position — area-level warning only
masmar.net derrotero de Euskadi
local knowledge — standard Basque bar-crossing practice
Electronic charts — A chart cannot express this. The danger is a function of tide state and swell, not of a charted depth.
Barre de l'Adour
CorroboratedConditional
Anglet / Boucau — mouth of the Adour
no published position
River bar at the Adour mouth, now trained between jetties. Between 1773 and 1814 it wrecked six ships a year. More than two thirds went ashore on the north side — there is a dominant current at the mouth setting vessels that way.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionA trained bar is still a bar. Cross on the flood, never on the ebb against swell, and allow for the set toward the north bank — that is where two thirds of the wrecks ended up.
Where this came from
No published position — area-level warning only
Bayonne municipal heritage archive — wreck statistics 1773–1814
regional maritime history
Electronic charts — The jetties are charted. The set toward the north bank is not.
Twelve petones (rocky heads)
Single source
Getaria — Gaztetape to Punta Irruarriaundieta
43°18.576′N2°12.947′W
The seabed from Gaztetape beach to Punta Irruarriaundieta (1 M at 297°) is stone, with twelve rocky heads inside the 4–6 m isobath. Published waypoint 43°18.576'N 002°12.947'W.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionStay outside the 10 m contour along this whole stretch.
Where this came from
Published waypoint
masmar.net derrotero de Euskadi, with waypoint
Bajo Cabana Arratzeco
Single source
Getaria — off Punta Irruarriaundieta
43°18.684′N2°13.050′W
200 m offshore
Shoal roughly 200 m NW of Punta Irruarriaundieta.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionGive the point a wide berth to seaward.
Where this came from
Computed from a published bearing and range — approximate
masmar.net derrotero de Euskadi
Bajo Chicharvel
Single sourceConditional
Hendaye — 660 m N of Playa de Hendaya
43°23.700′N1°46.200′W
13.0 m over it · 660 m offshore
Broad shoal with a least depth of 13 m among soundings of 25–30 m, about 660 m north of Hendaye beach. Published waypoint 43º 23,7'N / 001º 46,2'W.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding action13 m is no threat to a keel. It is a threat to a sea: a shoal that abrupt in 25–30 m will stand the swell up over it. Treat it as rough water, not as a grounding risk.
Where this came from
Published waypoint
masmar derrotero de Euskadi — with waypoint and soundings
Piedra Izarri
Single sourceConditional
Getaria — W shore of El Ratón
no published position
Rock that always shows except at spring high water, when it covers. Several others nearby behave the same way toward Gaztetape.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionAt spring highs the visual cue disappears. Do not navigate this stretch by eye on a big tide.
Where this came from
No published position — area-level warning only
masmar.net derrotero de Euskadi
Izustarri reef
Single sourceConditional
Getaria — Punta Izustarri
no published position
Izustarri throws off a reef to the NW where the swell breaks a long way from the shore.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionIn any northerly swell the break marks it. In calm it does not — and that is when boats cut the corner.
Where this came from
No published position — area-level warning only
masmar.net derrotero de Euskadi
The four passes
Single source
Saint-Jean-de-Luz / Ciboure — bay entrance
no published position
The bay has four passes through the Socoa, Artha and Sainte-Barbe breakwaters — L'Illarguita, Herreca, Belhara Perdun and the eastern pass. Only L'Illarguita is recommended, and it is the only one usable at night. Depths run −15 m on the west side but only −8 to −9 m on the east.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionUse L'Illarguita. The other three are local knowledge, and one of them is named after the shoal.
Where this came from
No published position — area-level warning only
French port guides (Bloc Marine / bateaux.com)
Electronic charts — All four passes are charted. Which one you may actually use is not.
Rocks off the Sainte-Barbe dike
Single source
Saint-Jean-de-Luz — eastern pass
no published position
Coming from the north into the eastern pass, rocks extend beyond the end of the Sainte-Barbe dike.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionDo not take the dike head as your turning mark. The foul ground runs past it.
Where this came from
No published position — area-level warning only
French port guides
Explosives dumping ground
Unverified
Offshore, N of the Hendaye → Saint-Jean-de-Luz route
no published position
Charted explosives dumping ground north of the direct route to Saint-Jean-de-Luz.
Locator only — no route is implied. Coastline from OpenStreetMap; hazard position as published. Stipple marks foul ground, not a surveyed extent.
Avoiding actionRoute south of it. Do not anchor or fish inside it.
Where this came from
No published position — area-level warning only
mibaluma.blogspot.com sailing log — «un vertedero de explosivos que dejamos un poco más al norte de nuestro rumbo»