Periodic sampling (twice per year) and analyses of the main elements, trace elements and isotopes, is carried out at the main hot springs and fumaroles of Nisyros (Avlaki and Loutra hot springs, fumaroles at Stefanos, Polyvotis Minor and Major and SE Ramos).

Considering all chemical, hydrology and hydrogeological parameters, Nisyros hot waters are possibly supplied by a) sea water subject to limited heating and mixed with ground-water; or b) heated ground-water mixed with sea water; or c) mixing of hot sea water and ground-water. In all cases, hot water is linked to relatively shallow water tables.

Nisyros fumaroles mainly emit a large percentage of heated ambient air and CO2. Moreover, very low and highly varying percentages of CH4, H2, CO are detected, and this indicates varying rates of mixing between the ambient air with a CO2-rich phase.

Over the entire period of monitoring, no significant variation in the chemical composition of hot gases or water has been recorded that could be interpreted as a process for re-activation of feeding by deeper magmatic fluids.