Data of a capture-mark recapture study of the Olm in the classic Karst used for the paper titled "Understanding benefits and risks of exploiting spring habitats by subterranean animals: insights from a mark-recapture study on the Olm (Proteus anguinus)".

From October 2022 to May 2023, we surveyed eight springs and three caves within the same area to capture and mark <i>Proteus anguinus</i> individuals. Moreover from 2 to 5 May, 2022, a total of 40 springs and 8 caves were selected for this activity and underwent extensive plankton and benthos measurements. Sampling was carried out during daylight hours.