This session, is taught by Jim Lukanich, CWT, describes how bacteria and other related microorganisms function in cooling water. This concept is then expanded into the formation of biofilm and the problems that biofilm can cause in a cooling system, as; deposit formation, under deposit corrosion, microbiologically induced corrosion (MIC), fouling and Legionellosis. The presentation will then cover the different treatment protocols (biocides, biostats and bio-dispersants) and how they may be used to control biological activity in a cooling water system.