Ostroumov S. A. Biological filtering and ecological machinery for self-purification and bioremediation in aquatic ecosystems: towards a holistic view. - Rivista di Biologia. 1998; 91(2): 221-232. http://scipeople.com/publication/99122/; PMID: 9857844 [PubMed - indexed for MEDLINE] According to one of approaches to the definition of criteria for the phenomenon of life, the key attribute is the ability of the life system for some self-regulating and self-supporting. Part of such holistic functions of aquatic ecosystems as self-regulating and self-supporting is their cleaning the water via a multitude of various mechanisms. The goal of this paper is to present some fundamental elements of the theory of ecosystem self-purification (water self-purification) which emphasizes the importance of the four functional biological filters that are instrumental in purification and upgrading the quality of water in aquatic ecosystems. These functional filters are: (1) direct water filtering by aquatic organisms that are filter-feeders; (2) the filter (represented mainly by communities of aquatic plants/periphyton) which prevents input of pollutants and biogenic elements (N, P) from land into water bodies and water streams; (3) the filter (represented by benthic organisms) which prevents re-entry of pollutants and biogenic elements from the bottom sediments into the water; (4) the filter (represented by microorganisms attached to particles which are suspended in the water) that provides microbiological treatment of the water column. New experimental data by the author reveal the negative role of man-made effects on the ecological machinery which purifies water. The analysis and discussion lead to the holistic theory of the natural process of bioremediation of aquatic ecosystems. Key words: self-regulating and self-supporting, aquatic ecosystems, theory of ecosystem self-purification, upgrading the quality of water, water filtering by aquatic organisms that are filter-feeders; communities of aquatic plants/periphyton, pollutants and biogenic elements (N, P), benthic organisms, microorganisms attached to particles which are suspended in the water, microbiological treatment of water column, man-made effects, natural process of bioremediation