The species occurs in karstic subterranean aquatic systems formed in limestone and dolomite rocks. It inhabits subterranean karstic habitats up to 1500 m vertical depth (dry cave systems with water streams at the bottom) and up to -113 depth of water column, withstanding water pressure of up to 12 atmospheres (Kovač-Konrad and Koller 2017). Many of the caves that the species occurs in are connected to rivers that run above ground for the first 50–100 km and then disappear into the ground. Subpopulations may be found close to the surface or as much as 300 m underground depending on the thickness of the karstic formation. It may also be found at cave entrances or washed-out of caves after episodes of high rainfall and flooding (Aljančič et al. 2014b).

The water temperature of the habitat ranges from about 5°C to 15°C, which is also the approximate extent of annual fluctuations. Proteus anguinus parkelj is found in warmer surface waters and some subpopulations of the nominal subspecies were found in such conditions as well. Animals feed on detritus and endemic cave invertebrates and hide in crevices or bottom sediment when disturbed, and are well adapted to cave life (e.g. Briegleb 1962, Aljančič et al. 1993, Bulog 2006, Balázs et al. 2015, Zakšek et al. 2017, Gorički et al. 2019). As it is very difficult to study the species in its natural subterranean habitat, most ecological data comes from cave laboratories (Briegleb 1962, Parzefall et al. 1980, Hervant et al. 2000). In captivity, they become sexually mature at 15 years of age and reproduce on average only every 12 years, while their lifespan can exceed 100 years (Voituron et al. 2011). Females lay up to 70 eggs on the undersides of stones (Briegleb 1962, Juberthie et al. 1996), and in some cases, the eggs are retained within the body and two fully formed young are produced.

This species is endemic to the European region, where it is restricted to subterranean aquatic habitats within the Dinaric Karst region of the Balkans, ranging from southern Slovenia and just across the border into adjoining northeastern Italy, through disjunct areas of western Croatia, and western Bosnia and Herzegovina, reaching the Trebišnjica River Basin in the south (e.g. Sket 1997, Jablonski et al. 2012, Koller et al. 2019, Kostanjšek et al. 2022). Environmental DNA of the species was also detected in western Montenegro (not mapped) (Aljančič et al. 2014a, Gorički et al. 2017), while the closest confirmed localities lie just across the border in Bosnia and Herzegovina. Its global AOO is 1,132 km² and the global EOO is 55,470 km².

Outside its natural range, the species has been introduced and naturalised in the subterranean basin of the Valstagna Caves near Oliero in northeastern Italy, which was populated from the Postojna-Planina Cave system in Slovenia in 1822 (Bressi and Dolce 2006). Captive subpopulations are maintained at the Subterranean Laboratory CNRS Moulis (France) and the Tular Cave Laboratory (Slovenia), and in the show caves, Postojna Caves (Slovenia), Hermannshöhle (Germany), Grotte de Choranche (France) and Baredine (Croatia).

Conservation Actions In-Place
This species is listed on Appendix II of the Bern Convention, and on Annexes II and IV of the EU Habitats Directive. It is recorded in the National Red Lists and is protected by national legislation in Italy, Slovenia, Croatia, Bosnia and Herzegovina, and Montenegro. In Slovenia, the subterranean habitat of the species is also protected by national legislation, and much of the range of this species is within Natura 2000 or other protected areas (Hudoklin 2011). In Italy and Croatia parts of its range are also included in Natura 2000 (Koller et al. 2019). The subspecies Proteus anguinus parkelj is particularly in need of protection, as its habitat is limited to only a few karst springs in connection with subterranean networks in a very small geographic area. Rehabilitation centres for veterinary treatment of injured or ill specimens are organised in Slovenia and Croatia, and at the Trebišnjica River Basin in Bosnia and Herzegovina (Aljančič et al. 2016, Lewarne 2018, Koller et al. 2019).

Conservation Needed
Once the identity of the different conservation units is confirmed, they are likely to have highly restricted ranges, are likely to be threatened and will require specific conservation actions (K. Poboljsaj pers. comm. September 2019). Urgent action is needed particularly to reduce pollution in the habitat of subspecies P. a. parkelj (G. Aljančič, P. Trontelj, V. Zakšek and K. Poboljsaj pers. comm. December 2019) and, generally, to remove aquatic invasive species. There is also an urgent need for an EU (European Union) wide coordinated approach and implementation of the Bsal Action Plan by Gilbert et al. (2020), which was commissioned by the European Commission.

Research Needed
Further taxonomic work is required to confirm the identity of the different conservation units.Ecological research on lifespan and population needed.