The development of the concept of sea estuaries as separate geographic objects based on a strategy of interdisciplinary research and about 6 million non-equidistant observation data, subject to nonstationarity of estuarine processes and unstable anthropogenic load, made it possible to propose a universal structural and hydrological typification of estuaries; to establish their maritime boundaries in terms of the minimum values of water salinityas Cv, to regionalize water areas from river to maritime boundaries and, on the this basis, to improve scientific terminology. Modern distribution schemes have been obtained and general patterns have been established for the variability of the main characteristics of the state of estuaries, depending on the variability of the river runoff and the water level of estuarine seasides, and new methods for their calculation, invariant for similar estuaries, are proposed. 54 negative phenomena are included in the catalogue; their interrelationships, causes and consequences are established. The analysis of estuarine processes has been carried out, the patterns of variability of their main characteristics from natural and anthropogenic factors have been determined. The ways of solving the problems of nature management in the estuarine regions of the northwestern part of the Black Sea are proposed. The monograph is intended for oceanographers, hydrologists, hydrochemists, ecologists, workers of environmental protection, monitoring and control organizations, as well as teachers, graduate students and students of relevant specialties.