This paper deals with some basic manifestations, methods and techniques applied in the system of technical observation of a hydro-electric power plant. Technical observations include hydrolologic forecast, surveying of buildings and monitoring of the installed machines and electric-power equipment. Basic for proper and cost-effective maintenance of a hydro-electric power plant is founded on familiarity with situation and on monitoring changes on buildings, plant and installed equipment. Proper maintenance in the plant contributes to its high operating safety and to its reliability whereas a hydro- -electric power plant is made disposable to a maximum degree. This paper concentrates on methods and procedures which give a clear picture of the state of buildings and equipment. Methods and procedures of testing and measurement dealt with in this study are neither harmful nor destructive considering equipment. Therefore, this piece of work above all considers practical, applicable and proved methods and procedures implemented in Croatian Power Utility (HEP) which are based on efective standards and instructions. Due to comprehensiveness of the problem area it is impossible to describe all the well-known methods and procedures of examination and measurement. All-embracing structure of the technical observation of hydro- -electric power plants is impossible to be entirely defined owing to specific quality of each object in terms of system, environment and technology.