In this book a brief description of monitoring systems of the most developed countries of the world (the USA, Canada, European states) and Global Environment Monitoring System (GEMS/WATER) is given. A structure of a state monitoring system of inland surface waters of the Russian Federation including the subsystems of surveillance, operational and special types of monitoring is considered in detail. A large section of the book is dedicated to the results of full-scale ecological modelling and a study of intrabasin processes as a basis for ecological standardisation. A methodology for complex assessment of water quality is analysed and the most recognised and official method in Russia for complex assessments of ISW pollution level is described.