Though naturally rare, wetland biotopes on small Greek islands have great significance for biodiversity there and for migrating animals. Anthropogenic influences are diminishing these habitats, and climate change is accelerating their decline. This is exemplified for Kythnos with reference to the occurrence of the Balkan terrapin (Mauremys rivulata) and the Balkan frog (Pelophylax kurtmuelleri). The hydrologic catchments were searched for their occurrence in late May/early June 2021. Most of the former known populations have disappeared, and those that remain are extremely vulnerable, so that these species are likely to become extinct on Kythnos.