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Hotels, dive operators, gear, and how to get here are on the Ari Atoll location page.
Overview
Hranice Abyss is the deepest known flooded freshwater cave in the world, located in the Moravian Karst region of the Czech Republic. This impressive geological formation offers a unique technical diving experience into its vast submerged passages and chambers, revealing stunning rock formations and an unparalleled sense of exploration into the Earth's depths.
Briefing note
Strict permits and specialized technical diving certification required. Diving is typically conducted with authorized exploration teams.
What you'll see
1 species curated- year-roundCave FaunaPeak: Jan · Feb · Mar · Apr · May · Jun · Jul · Aug · Sep · Oct · Nov · Dec
Sightings evidence
1 record on file- medium confidenceCave Fauna
- Last confirmed
- Jun 2024
- Recent records
- 5 within 1 km
- Cluster months
- Year-round
Presence of unique cave-dwelling organisms adapted to aphotic, oligotrophic conditions.
Sources & methodology
How we summarise this
We aggregate confirmed occurrence records from GBIF and OBIS within a fixed radius of each dive site. Occurrence records confirm presence and reveal seasonality clustering, but they DO NOT measure per-dive probability — there is no eligible-effort denominator. We deliberately do not publish a numeric '% chance of sighting' from this data.
Sources
- Global Biodiversity Information Facility — GBIF Secretariat
- Ocean Biodiversity Information System — IOC-UNESCO
- OBIS-SEAMAP — Duke University Marine Geospatial Ecology Lab / OBIS
- iNaturalist — California Academy of Sciences & National Geographic Society
- IUCN Red List of Threatened Species — International Union for Conservation of Nature
- WoRMS — World Register of Marine Species — Flanders Marine Institute (VLIZ)
- FishBase — FishBase Consortium
- Atlas of Living Australia — CSIRO / GBIF Australia
- REEF Volunteer Fish Survey — Reef Environmental Education Foundation
Conditions
| Month | Water | Visibility | Current |
|---|---|---|---|
| Jan | 8–10 °C | 20–40 m | none |
| Feb | 8–10 °C | 20–40 m | none |
| Mar | 8–10 °C | 20–40 m | none |
| Apr | 8–10 °C | 20–40 m | none |
| May | 8–10 °C | 20–40 m | none |
| Jun | 8–10 °C | 20–40 m | none |
| Jul | 8–10 °C | 20–40 m | none |
| Aug | 8–10 °C | 20–40 m | none |
| Sep | 8–10 °C | 20–40 m | none |
| Oct | 8–10 °C | 20–40 m | none |
| Nov | 8–10 °C | 20–40 m | none |
| Dec | 8–10 °C | 20–40 m | none |
Season calendar
Next step
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