## 5 Conclusions  
The main objective of our study was to demonstrate the main thematic applications of highly-detailed remote sensing data in visible and thermal spectra, obtained as a result of repeated surveys from small UAVs, in the integral system of prompt and regular monitoring of highly dynamic and vulnerable coastal zone of Lake Sevan under diverse anthropogenic impacts and an artificially changing water level. We have elaborated and tested several techniques and protocols of surveys depending on thematic tasks: flights at different heights and in different seasons. The advantage of thermal surveys above optical ones is more accurate identification of coastal wetlands' state and structure. Thermal UAV surveys can be considered as a prospective technology for rapid detection of illegal sewage as well as dead biomass in degraded and submerged habitats. Our results have shown a very uneven character of anthropogenic impacts in coastal ecosystems by type and level along the shorelines of Minor Sevan and Major Sevan. Resulting from low environmental responsibility of local people and tourists, such environmental violations as illegal land development, direct discharge of raw sewage, fish poaching, and unsound practices of aquaculture, extensive spontaneous clumping of anthropogenic litter along the coasts should be traced and resolved by means of UAV-derived multi-temporal data with ultra-high spatial resolution. As a result of multi-temporal UAV data analysis, we found out that the high rate of shore erosion (more than 3.5 m per year in some places) and rapid degradation of waterlogged or submerged habitats with decaying biomass promote eutrophication and strong algal blooms. The more vulnerable present-day coastal types with endangered habitats are erosional and marsh coasts, accounting for 28.1% and 10.1%, respectively, of the total shoreline of Lake Sevan. The water rises to 1903.5 m by 2030,as intended by national legislation can lead, according to our large-scale mapping and spatial analysis, to the complete flooding of road sections, important recreational facilities, and valuable forested areas along the Sevan coasts. Under the definite advantages of UAV data for specific tasks at the large-scale level and their flexibility of operative or on request acquisition, the UAV-based environmental coastal monitoring of complex and highly dynamic area should become a necessary intermediary between field measurements and satellite RS data in a multi-scaled, multi-temporal, and multi-platform integral scheme for monitoring the coastal zone and water body of the whole Lake Sevan under unprecedented changes in its water level and associated environmental issues and challenges. Approaches and findings presented in this paper can also be implemented for environmental monitoring and coastal management of high- mountainous large lakes or reservoirs in regions with limited water resources. Conceptualization, A.M. and N.T. Methodology, A.M. and A.K. UAV data acquisition and software, A.M. and P.K. Validation, N.T., N.A., P.K., S.A., and A.N. Formal analysis, N.T. and N.A. Data curation, A.M. Writing--original draft preparation, A.M., N.T., N.A., A.K., S.A. and A.N. Writing--review and editing, A.M., N.T. and A.K. Visualization, A.M., N.T., and P.K. All authors have read and agreed to the published version of the manuscript. This work was supported by the State Committee of Science (SCS) of the Ministry of Science, Education, Culture and Sport of Armenia, and Russian Foundation for Basic Research (RFBR) in the frames of joint research project SCS 18 RF-140 and RFBR 18-55-05015 (field studies and UAV surveys in 2018-2019). Additional support was provided by the Institute of Geography, Russian Academy of Sciences, State Assignment number AAAA-A19-119022190168-8. The authors are grateful to [PERSON] who did the proof-reading of the text as well as to the four anonymous reviewers for their valuable comments on the previous versions of the manuscript.