The comprehensive analysis of the "hydroecosystems' health" concept was carried out; various views on this concept were considered in view of modern approaches to the natural water bodies' state assessment. The application of this concept in the monitoring programs and national legislation regarding the water resources' protection and management was analyzed. The evolution of the concept of "hydroecosystems' health" and search for indicators of its diagnostics was shown. The generalization of the analyzed information enabled to suggest the original definition of the concept of "hydroecosystems health", including all its aspects.

Studying fish growth is a complex task because growth depends on many factors. The process of fish growth is influenced by ecological factors of the water environment. Each species of fish has growth characteristics and characteristic changes in this process as a result of the action of natural and anthropogenic factors. We investigated the morphometric features of Scardinius erythrophthalmus in the hydroecosystem conditions of the Horyn River. Fish were caught by amateur fishing methods during 2018–2021 in the section of the hydrographic system of the Horyn River within the Rivne Plateau, which is the northern part of the Volhynian Upland , namely the Horyn River and its tributaries – the Zamchysko River, the Ustia River, and the Stubelka River. The catches included fish aged from 0+ (one-year-olds) to 5+ (five-year-olds). Growth variability was studied for fish aged 1+ to 4+ because their numbers were sufficient for statistical evaluation. We noticed clear features of the morphometric variability of the fish. According to the coefficient of variation for the general populations of S. erythrophthalmus from different rivers, there was mostly significant variability of such growth characteristics as the largest and smallest fish body height, total length, Smith length and short body length of fish. We also noticed the similarity of the morphometric variability of fish of different ages for the Horyn River and Stubelka River and Zamchisko River and Ustia River. The analysis and evaluation of the surface water quality of these rivers was also similar. Thus, Horyn and Stubla districts had a transitional state from II to III quality class, and the Zamchysko River and Ustya River districts had a transitional state from III to IV quality class. We conducted a multivariate regression and it revealed statistical significance and a close correlation between the coefficients of variation of the growth characteristics of fish with the phosphate content in the water (with an average value of the weighting coefficients of 0.50 ± 0.06), nitrite nitrogen (0.39 ± 0.10) and nitrate nitrogen (0.84 ± 0.34). The calculation of the specific growth of fish by full length revealed that the intensity of growth is the highest between the first and second year of life of fish for small rivers (Zamchysko River, Ustya River, Stubelka River) and between the second and third year for the Horyn River. The results presented in the article are valuable and describe the local variation in the morphometric variability of S. erythrophthalmus. This expanded the understanding of the influence of ecological factors of the aquatic environment on the formation of growth characteristics of this species of fish. In the future, our research will continue and study the linear growth of natural fish populations against the background of changes in the ecological and hydrological conditions of the studied region

Наукова новизна. З'ясовано сучасний стан структурно-функціональної організації угруповань літорального зоопланктону верхів'я Кременчуцького водосховища. Практична значимість. Проведені дослідження дають уявлення про структурнофункціональну організацію угруповань літорального зоопланктону верхів'я Кременчуцького водосховища в районі Канівського заповідника, що уможливлює прогнозування подальших змін угруповань зоопланктону, оцінювання стану екосистем та розрахунок кормової бази молоді риб.

The analysis results of the structural-functional organization of littoral zooplankton community of the upper Kremenchug Reservoir in the territory of Kaniv Nature Reserve during the summer of 2015 are presented. Diversity of zooplankton was presented with 34 species: Monogononta rotifers, cladocerans, copepods. The rotatoria-cladoceran zooplankton complex dominated in the taxonomic composition. Zhakkara dominant index for the comparison of the dominant species complexes was used, and it was the low number of similarities within the various biotopes of the six research stations (J = 7,1-28,6). This can be explained by the formation of higher aquatic plants.This led to the formation of specific zooplankton groups in overgrown biotopes.The ecological spectrum of the different groups of the upper Kremenchug Reservoir littoral zooplankton in the summer was characterized by the predominance of the phytophilic groups: phytophilic – 18 species (53 % of all zooplankton species). Depending on the feeding type the largest part was made by the peaceful group – 73,3 % (25 species). Summer littoral zooplankton in quantitative terms was characterized by very low development in both biotopes. Its density varied within 4077± 2098 ind./m³ and biomass 0,07 ± 0,04 g/m for overgrown biotopes, and 4123 ± 3929 ind./m³ and 0,054 ± 0,038 g/m³ for freshwater ones. Among the quantitative indicators, the species of Copepoda dominated, what was associated with the development of their larval stages (Nauplia, Сalanoida juv., Cyclopoida juv.) in the summer period.

The scale of military operations in Ukraine has no analogues since the Second World War, therefore it is absolutely necessary to find out their impact on the environment both for further lawsuits against the aggressor country and for the development of measures to restore ecosystems damaged by military operations and ensure health of the population.The aim is to assess the impact of various types of military operations on the state of hydroecosystems of Ukraine, to determine the damage caused to them and to develop a system of measures to restore them.The results of the research will allow to quantify the consequences of the military operations impact on the ecosystems in a new way and develop a system of restoration measures for ecosystems that have been strongly affected by military operations to varying degrees, and ensure that the level of water quality is determined to preserve the health of the local population. Moreover, it will make a significant contribution to the development of the ecosystem functioning theory under martial law and military operations.