The paper aims to investigate the distribution and evolution of toponyms derivative of the words „iezer” and “bolătău” (Romanian) and their counterparts in the neighboring countries, where such homologous words/toponyms exist, i.e. Poland, the Czech Republic and Slovenia. We documented that at present the terms where the toponyms originated (“iezer”/”jezero”/”jezioro” and “bolătău”/”blato”/ ”błoto”) are largely regarded as archaic forms, particularly “bolătău”/ ”blato”/”błoto” throughout the study area. However, toponyms based on both words are still in use in a large number of derivative variants (especially in the Slavic-speaking countries), which attest their age and relevance in the toponymical practice, albeit to a different extent and with national and regional variations in terms of occurrence. The study also indicates that, whereas the research topic requires further exploration in the shape of a quantitative approach investigation, given the complexity of toponymical studies within such an extensive area, it can be inferred that currently the vast majority of toponyms based on the two terms do not refer to water bodies, but have been transferred to other elements of the landscape.