**5. Conclusions**

The comparison between three periods of investigations of the alpine Nesamovyte lake: 1910–1920, 1967–1978 and 2013–2021 revealed significant structural changes in its taxonomic composition of algae, as well as a complex of leading genera and species.

Ecological analysis of the species composition of algae was based on its ecological characteristics and confirmed specific changes that took place with the ecosystem of the lake during different historical periods. The changes in hydrological characteristics, species diversity of algae, systematic structure, communities of dominant and indicator species, the trophic state and organic pollution over a 100-year period revealed the anthropogenic influence in the ecosystem of the lake. The obtained results confirmed the opinion [42,129–131] on the sensitivity and vulnerability of this type of water bodies and its role as an early response-indicator to a change in climate, environmental conditions and an increased level

of anthropogenic impact, as well as the need for efforts to preserve this ecosystem of the Eastern Carpathians.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/d13060256/s1, Table S1: Species composition and ecological preferences of algae and cyanobacteria of the Nesamovyte Lake in three studied periods (1910–1920; 1967–1978; 2013–2021).

**Author Contributions:** Conceptualization, P.M.T. and O.P.B.; validation, P.M.T., O.P.B., S.B.; investigation, O.M.K.-Z. and H.H.L.; writing—original draft preparation, P.M.T. and O.P.B.: data curation, P.M.T.; writing—review and editing, P.M.T.; visualization, S.B., O.M.K.-Z.; supervision, P.M.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** Species composition and ecological preferences of algae and cyanobacteria of the Nesamovyte Lake in three studied periods are available in Supplementary Table S1.

**Acknowledgments:** The authors acknowledge financial and organizational support given by the administration and the employees of the National Academy of Science of Ukraine and Academy of Science of Poland for financial support of the Polish-Ukrainian project of scientific cooperation. We are grateful to I.I. Chorney, V.V. Budjak and O.I. Khudyi (Yuri Fedkovych Chernivtsi University), as well as T. Mykitchak (Institute of Ecology of the Carpathians of the NAS of Ukraine, Lviv) for organizing and conducting field trips to the Ukrainian Carpathians and for assistance in the work. Our gratitude extends to J. Tunovsky (Institute of Freshwater Fish Research, Poland) for the provided hydroecological indicators. Also, authors are very grateful to Taras Kazantsev and Trevor Williams for the proofreading of the English text.

**Conflicts of Interest:** The authors declare no conflict of interest.
