Mountain water objects (MWO) are very dangerous complex objects, where local and global natural and man-made catastrophes can result in huge negative and irreversible damage to the environment and the population. The main processes, initiation and evolution of critical phenomena at MWO are under consideration, including a model for its risk and damage assessments, MWO classification on their dangerous degrees, risk management, development of counter measures for prediction/prevention of the catastrophes and reducing of negative effects.