The biosphere of our planet exists in the form of living organisms and products of their vital activity in the gaseous shell of the Earth. More than75% of the total surface area of the planet is occupied by the water surface. This book studies the structure and functioning of aquatic ecosystems. The book tackle the individual aquatic organisms, their populations and communities, interactions between them and with inanimate nature.Aquatic ecology is a part of geoecology that studies aquatic ecosystems as a set of three interacting components: the aquatic environment, aquatic organisms and human activities. Hydrobiology and aquatic ecology are closely related, first of all, with the sciences of the hydrosphere - hydrochemistry, hydrophysics, hydrology.