Slovenia – Lakes, Rivers & Caves

Slovenia's freshwater diving is mostly small, clear and cold. The Soča and its tributaries (Idrijca, Bača, Idrija, Nadiža) cut pools and short gorges with marble trout and carved rock, down to the drowned gorges of the hydropower reservoirs at Most na Soči, Kanal and Solkan; the Vipava, the Krka and the Kolpa have warmer, gentler pools and weirs. Lakes range from Bohinj and Bled to reservoirs in the Brkini hills, the intermittent lakes of Cerknica and Pivka, and the 40 m-deep flooded coal-mine lake at Kočevje. Most open-water sites come from the Slovenian Diving Federation's atlas, which publishes positions and site sheets. Beneath the Classical Karst lie some of Europe's deepest sumps – Divje jezero, the Postojna–Planina system, Križna jama, Dobličica – but every cave is protected by the Cave Protection Act and these are dived only by club research teams; there is no commercial cave diving. Places where diving is banned (the high lakes and Velika korita in Triglav National Park, Zelenci, Krupa) are listed and clearly marked so you know not to go.

Facts

• Soča water temperature: Upper and middle Soča: about 4 °C in winter and only about 10–12 °C in summer (Kršovec, Velika korita, Kobarid); lower Soča reservoirs (Kanal, Plave, Solkan) reach about 15–16 °C in summer. Best visibility is in winter, warmest water in summer; dive only at low water.
• Alpine lake temperature: Lakes Bohinj and Bled: surface up to about 25 °C in summer but about 4 °C at depth, with a sharp thermocline; life is concentrated at 2–7 m. Lake Velenje is about 4 °C at all depths in winter (regulator-freeze risk).
• Triglav National Park – diving rules: ZTNP-1 (2010): in the park's first protection zone swimming, diving and boating on lakes and watercourses are prohibited (Art. 15(1)(17)); across the park, sport/recreation on waters is allowed only at designated places with the manager's consent (Art. 13(1)(48)); in the Lake Bohinj area (second zone) swimming, diving, skating, boating and sailing are expressly allowed (Art. 16(2)(4)). The park (2012 letter published by SPZ) states: Lake Bohinj – diving without consent; Soča gorge at Kršovec – only with consent; it objected to recommending Velika korita and the high-mountain lakes (Krn, Lužnica, Črno, Dvojno, Kriška jezera). Fines from €500 (individual).
• Fishing waters on the Soča: The Soča valley's fishing districts are managed by the Slovenian Fisheries Institute (upper Soča, Koritnica, Lepena) and Ribiška družina Tolmin (lower Soča and most tributaries); fly fishing only, with catch-and-release sections. No source found requiring divers to obtain fishing-club consent, but anglers are common at river sites (e.g. Idrsko) – give them space and never touch hooked fish.
• River diving planning – water level: Soča dives are only feasible at low water; for Kobarid the atlas suggests the ARSO gauge at Log Čezsoški below ~50 cm and flow below ~10 m³/s. On the lower Soča (Kanal, Plave, Solkan) flow depends on hydropower plants – the Solkan plant usually runs at peak hours, so afternoons are calmer. Kayaks and rafts share the river.
• Emergency number: 112 – ambulance, fire brigade, mountain and cave rescue and other rescue services; 113 – police.
• Recompression chamber: No official source was found confirming a 24/7 recompression chamber in Slovenia. A Slovenian diver with decompression sickness was treated in the hyperbaric chamber of the hospital in Rijeka, Croatia (2022 news report). Confirm current options with 112 / DAN before diving.
• Caves are state-owned and protected: Under the Cave Protection Act (ZVPJ, Ur. l. RS 2/2004) a cave is any natural void longer or deeper than 10 m, dry or permanently/periodically water-filled; caves are natural values of national importance, natural public good and state property (Arts. 2, 5). Slovenia has 21,502 natural values, 16,236 of them caves.
• Entry regimes: Caves are classified as open with free entry, open with controlled entry (supervised and registered entry) or closed. Closed caves may be entered only for scientific research or archaeological work with a permit from the ministry, under the expert supervision of the nature-conservation organisation (ZVPJ Art. 17).
• Who may explore and dive caves: Discovering and exploring caves (including sumps) is reserved for persons certified for independent caving; the Speleological Association of Slovenia (JZS) checks the training. Explorers have free entry to open caves but must notify the cave's custodian, concessionaire or protected-area manager in time (Art. 14). Motorised craft are banned in caves except electric underwater scooters used to explore sumps (Art. 18). There is no tourist cave-diving permit: all cave dives in this region are done by club research teams.
• Permit authority: The ministry responsible for nature conservation – currently listed on gov.si as the Ministry of Environment and Spatial Planning, Nature Conservation Sector (Dunajska cesta 47, Ljubljana, +386 1 478 73 35) – issues permits for closed caves and exceptional activities in caves and runs custodian (skrbnik) contracts for 22 caves; the Institute of the Republic of Slovenia for Nature Conservation (ZRSVN) gives expert opinions on classification.
• Cave register: Anyone who discovers a possible cave or cave passage must report it to the Karst Research Institute ZRC SAZU, which holds this task as a public mandate and verifies the data (ZVPJ Arts. 8–9). Clubs and the JZS also keep their own cave cadastres.
• Cave rescue and emergency: Call 112 for all rescue services, including cave rescue. Sump accidents are handled by the Cave Rescue Service (Jamarska reševalna služba, JRS) together with the state technical-diving unit; the December 2025 Škocjan recovery involved 72 cave rescuers and lasted 16 hours. The two units trained together in the Bilpa spring cave in 2022.
• The olm (Proteus anguinus) is strictly protected: The olm ('človeška ribica'), a Slovenian national symbol endemic to the Dinaric Karst, is protected as an Annex II priority species of the EU Habitats Directive. Sources in this region report it in the Pivka jama sumps (a large colony), Divje jezero and Krška jama; the black olm (Proteus anguinus parkelj) is known from the Dobličica spring. Never touch, disturb or collect olms; cave fauna is also protected by ZVPJ.
• No commercial cave diving: No commercial dive centre offering guided cave or sump dives in Slovenia was found. Every cave site in this region is dived only by volunteer caving/cave-diving teams under ZVPJ; visiting cave divers should contact the clubs and the JZS rather than expect bookable dives.
• Cave water temperatures: Cave and spring water is cold all year: Divje jezero 7–10 °C, Planinska jama 8–10 °C (about 5 °C in the sump in January 1964), Križna jama about 8 °C, Krupa spring about 10 °C in summer; in Podpeško jezero about 15 °C in the deep shaft under a ~25 °C summer surface. Drysuits are standard.

Season

• Best months: May, Jun, Jul, Aug, Sep
• Acceptable: Apr, Oct
• Poor: Nov, Dec, Jan, Feb, Mar
• Water temperature: 4–22 °C

Alpine lakes and quarries: PADI gives May to September as best (12–22 C depending on depth). Winter is cold with occasional ice, and snowmelt clouds the water in early spring. No lake-specific data for Bled/Bohinj, general Slovenian source.

Dive sites (107)

Soča Valley (Bovec – Kobarid – Solkan)

• 'Luknja' hole in the Soča at Plave – 0–24 m, intermediate
• Bača gorge at Klavže (Podmelec) – 0–4.5 m, intermediate
• Idrija river pool at Golo Brdo – 0–3 m, beginner
• Idrija river pools at Podravno – 0–4 m, beginner
• Idrija river pools at Zarog – 0–4 m, intermediate
• Klonte weir pool on the Bača – 0–3.5 m, beginner
• Kozjak waterfall pools (Kobarid) – 0–5 m, beginner
• Krčnik Gorge with natural bridge (Kožbanjšček, Goriška Brda) – 0–6 m, intermediate
• Most na Soči – Soča–Idrijca confluence – 0–30 m, advanced
• Nadiža under the Napoleon Bridge (Robidišče) – 0–5 m, beginner
• Plužna reservoir and Virje waterfall (Bovec) – 0–4.5 m, intermediate
• Slatna stream pool at Grgar – 0–4 m, beginner
• Soča at Dermota – 0–13 m, beginner
• Soča between Doblar and Podselo – 0–4 m, beginner
• Soča gorge at Kršovec (Bovec) – 1–6 m, advanced
• Soča pool at Idrsko – 0–3 m, beginner
• Soča pools at Deskle – 0–11 m, beginner
• Soča pools below Tonocov grad (Kobarid) – 0–6 m, intermediate
• Soča under Napoleon Bridge (Kobarid) – 0–10 m, intermediate
• Soča under the bridge in Kanal – 0–14 m, intermediate
• Soča under the Solkan bridges – 0–10 m, intermediate
• Soča–Tolminka confluence (Tolmin) – 0–5 m, beginner
• Učja pools at Žaga – 0–5 m, beginner
• Velika korita Soče (TILOS / no diving) – 0–8 m, advanced

Central & East Slovenia (Ljubljana area, Velenje)

• Borovniščica pools in Pekel gorge – 0–3.3 m, advanced
• Godovič pond at Šebalk – 0–3.5 m, beginner
• Lake Velenje – at the boathouse – 0–15 m, intermediate
• Podpeško jezero – 0–25 m, advanced
• Verd clay-pit lakes (Vrhnika) – 0–7 m, beginner

Vipava valley & Karst (Škocjan)

• Branica pools at Zavivalca gorge – 0–3 m, beginner
• Reka pools before Škocjan – 0–5.5 m, beginner
• Reka river below the Škoflje bridge – 0–6 m, beginner
• Vipava at Batuje weir – 0–4.5 m, beginner
• Vipava at Bilje (old mill weir) – 0–7 m, beginner
• Vipava at Kasovlje mill – 0–3.5 m, beginner
• Vipava at Miren (Pri Selu weir) – 0–6 m, intermediate
• Vipava at Miren (town centre) – 0–7 m, beginner
• Vipava at Renče (Christmas dive) – 0–7 m, beginner
• Vipava at Steske (Pekel gorge) – 0–4 m, beginner
• Vipava at Uhanje (Dulanov mlin) – 0–3.5 m, beginner
• Vipava meander at Dombrava – 0–5 m, beginner
• Vogršček reservoir – 0–6 m, beginner
• Volčja Draga clay-pit lake – 0–3 m, beginner
• Škocjanske jame – Reka sumps (Ledeni dihnik, Marchesetti lake) – 0–21 m, advanced

Notranjska & Brkini (Cerknica, Postojna, Pivka)

• Cemun and Obrh springs (Lake Cerknica) – 0–5 m, beginner
• Kotliči springs and Rak river (Rakov Škocjan) – 0–10 m, advanced
• Križna jama / Nova Križna jama – deep sump – 0–153 m, advanced
• Lake Cerknica – Rešeto sinkholes – 0–10 m, beginner
• Lake Cerknica – Stržen under the bridge – 0–4 m, beginner
• Lake Klivnik (Brkini) – 0–24 m, intermediate
• Lake Mola (Brkini) – 0–16 m, intermediate
• Lake Rakitna – 0–3 m, beginner
• Nanoščica at Cenetov mlin – 0–3 m, beginner
• Palško Lake (Pivka intermittent lakes) – 0–10 m, beginner
• Parsko & Drskovče lakes (Pivka intermittent lakes) – 0–2 m, beginner
• Petelinjsko Lake (Pivka intermittent lakes) – 0–10 m, beginner
• Pivka jama – outflow sumps of the underground Pivka (Postojna system) – 0–30 m, advanced
• Planinska jama – Pivka branch sump – 0–50 m, advanced
• Unica under the old bridge at Haasberg – 0–4 m, beginner

Idrijca valley & Idrija

• Divje jezero (Wild Lake) – 0–160 m, advanced
• Idrijca at Dolenja Trebuša – 0–4 m, beginner
• Idrijca at Slap ob Idrijci – 0–5 m, beginner
• Idrijca gorge at Mlinšče – 0–4 m, beginner
• Idrijca gorge at Most na Soči station – 0–11 m, intermediate
• Idrijca pool at Laze (Reka) – 0–6 m, beginner
• Idrijca pools at Kurnik – 0–7.5 m, beginner
• Idrijca pools at Oblaz – 0–5 m, beginner
• Idrijca pools below the Skvarč farm – 0–6 m, beginner
• Idrijca – weir at Kobila (Zgornja Idrijca Landscape Park) – 0–6 m, beginner
• Lower Gačnik pools (Trebuša) – 0–4.5 m, intermediate
• Ovčjaške klavže reservoir (Kanomlja) – 0–10 m, intermediate
• Pršjak waterfall pools (Trebuša) – 0–3 m, intermediate
• Trebuščica pools below Podkobilški most – 0–2 m, intermediate
• Ušnik dam pool at Podsela – 0–12 m, intermediate

Julian Alps & Gorenjska (Bohinj, Bled)

• Dvojno jezero (Triglav Lakes Valley) (TILOS / no diving) – 0–8.7 m, intermediate
• Kamniška Bistrica spring pool – 0–3 m, intermediate
• Kriška jezera (TILOS / no diving) – 0–8.5 m, advanced
• Lake Bled – Castle Bathing Area – 2–10 m, beginner
• Lake Bohinj – Kramar – 2–20 m, beginner
• Lake Bohinj – Naklova glava – 2–25 m, beginner
• Lake Jasna (Kranjska Gora) – 0–2.5 m, beginner
• Lake Javornik (Javorniški Rovt) – 0–3.6 m, intermediate
• Lake Krn (Krnsko jezero) (TILOS / no diving) – 0–16 m, intermediate
• Lake Lužnica (Krn mountains) (TILOS / no diving) – 0–8 m, intermediate
• Lake Planšar (Zgornje Jezersko) – 0–2 m, beginner
• Lake Završnica (Žirovnica) – 0–8 m, intermediate
• Lake Črnava (Preddvor) – 0–6.5 m, beginner
• Sava Bohinjka gorge at Ribčev Laz – 0–10 m, advanced
• Zelenci springs – source of the Sava Dolinka (TILOS / no diving) – 0–3 m, intermediate
• Črno jezero (Triglav Lakes Valley) (TILOS / no diving) – 0–8.5 m, advanced

Dolenjska & Bela krajina (Krka, Kolpa, Kočevje)

• Izvir Bilpa (Bilpa spring cave) – advanced
• Izvir Dobličice (Dobličko jezero spring) – 0–121 m, advanced
• Izvir Krupe (TILOS / no diving) – 0–7 m, advanced
• Jama Poltarica (Krka tributary spring cave) – 0–13 m, advanced
• Kolpa at the Rosalnice bridge (Metlika) – 0–5 m, beginner
• Kočevje Mine Lake (Rudniško jezero) – 0–40 m, advanced
• Krka at Otočec castle – 0–3 m, beginner
• Krka in Novo mesto (season-opening dive) – 0–4 m, beginner
• Krka pools at Zagradec – 0–7 m, beginner
• Krka tufa pools at Dvor – 0–10 m, beginner
• Krška jama – Krka spring sump – advanced
• Lake Bloke (Bloško jezero) – 0–3 m, beginner
• Lake Reško (Kočevska Reka) – 0–4.5 m, beginner
• Lukenjska jama (cave below Luknja castle) – sump – advanced
• Ribnica springs (former fish farm pools) – 0–3 m, intermediate
• Sand-pit lake at Male Rebrce (Pajčna) – 0–8 m, beginner
• Temenica at Luknja near Prečna – 0–3 m, intermediate

Operators (4)

• DPD Bled (Društvo za podvodne dejavnosti Bled) – club, Castle Bathing Area, Veslaška promenada 11, Bled (Slovenia)
• Potapljaški klub Mehurček – club, Nova Gorica (Slovenia)
• Jamarski klub Novo mesto (JKNM) – club, Novo mesto (Slovenia)
• Društvo za raziskovanje jam Ljubljana (DZRJ Ljubljana) – club, Ljubljana (Slovenia)

Most positions come from the Slovenian Diving Federation atlas, whose sheets date from 2005–2017: river depth changes with every flood, and access, rules and contacts may have changed. Dive rivers only at low water and watch for kayaks and rafts. Sites marked TILOS / no diving are listed for information only – do not dive there. Caves and sumps are protected and dived only by permitted research teams; they are not open to visiting divers.