Burgundy
Fosse Dionne
Closed to divers
Diving banned by municipal order since the fatal accident of June 1996. The town of Tonnerre only grants exceptional permission for exploration and survey work.
- Max depth79.5 m
- CertificationFull cave
- SpecialSidemount
Diving and fills
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Now at Fosse Dionne
What it looks like
Fosse DIONNE TONNERRE - PLONGÉE Tonnerre : un plongeur reprend l’exploration de la mystérieuse fosse Dionne Tonnerre : un plongeur bat un record de profondeur en explorant la mystérieuse fosse Dionne La Fosse Dionne : plongée dans un mystère qui intrigue depuis des siècles
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Videos and posts
From other divers, via YouTube, Instagram and Facebook. They only load when you click; after that, Google's or Meta's privacy rules apply.
Fosse DIONNE TONNERRE - PLONGÉE Tonnerre : un plongeur reprend l’exploration de la mystérieuse fosse Dionne Tonnerre : un plongeur bat un record de profondeur en explorant la mystérieuse fosse Dionne La Fosse Dionne : plongée dans un mystère qui intrigue depuis des siècles
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Other people's footage, not advice: how someone else dives here says nothing about what suits your team. Dive within your training.
The dive
A turquoise karst spring. Visibility was historically often reduced by suspended clay. Mean discharge is 311 l/s (87 l/s in August, 619 l/s in January, 3,000 l/s in the flood of 15 March 2001).
1 earlier accident or incident has been reported at this cave. Read what happened ↓
Profile and sections
A turquoise karst spring. Visibility was historically often reduced by suspended clay.
Mean discharge is 311 l/s (87 l/s in August, 619 l/s in January, 3,000 l/s in the flood of 15 March 2001). The first known exploration was in 1955. The spring has been a monument historique since 1920.
Practical: the town grants permission for exploration only in exceptional cases (since 2018 to one cave diver).
- Depth and profile
- Entrance 2.5 m high, then down at 45° to -32 m; restriction of 0.8 × 0.4 m; -70 m at 370 m (1989); deepest point -79.5 m (October 2019).
- Configuration
- Diving banned. For the record: a dangerous restriction (0.8 × 0.4 m) and a series of deep sumps with long decompression.
- DPV: Not DPV-suitable (estimate)
- Off limits; narrow and deep as well.
Who can dive where
- At least Full cave
- Configurations: Backmount / twinset / Sidemount / CCR / Small cylinders / no-mount (speleo sumps)
- Goes down to 79.5 m (trimix or deco may be needed)
- Experienced divers only
This is how the planner decides who in your team may dive this cave. Rules your own trip adds (organizer, a mail, the AI) show with your trip.
How to get there
Town spring with a wash-house (lavoir) in the centre of Tonnerre, free to visit all year. Diving is prohibited.
Around Fosse Dionne
FillsNo fill station known nearby
Caves nearby1 within 45 km
News
All (1)
Accidents and incidents
What happened at this cave before, with the sources. No names are given; read it as a lesson for your own planning.
- Fatal diving accidents in 1962 and in June 1996; after the accident of 16 June 1996 the town banned all diving.
Access and rules change: check what applies locally right before your trip. Source: GDELT Project and the news feeds of diving magazines. Search for more news ↗ Searched automatically, last on 13 Nov 2026.
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