ABSTRACT
Cyanobacteria are amongst the most ancient groups of organisms on earth with calcareous accretions formed by cyanobacterial mats in the estuarine waters of Western Australia being more than a billion (1×109) years old[1]. Over 2000 species of cyanobacteria have been identified and can be found across all climatic zones in aquatic environments ranging in size from garden ponds to oceans. This chapter is concerned with the toxic bloom-forming cyanobacteria found in freshwater impoundments with relatively long retention times such as lakes and reservoirs and also in some rivers, particularly within dead zones. The most common bloom forming toxic cyanobacteria include Microcystis, Anabaena, Oscillatoria and Aphanizomenon and like all cyanobacteria these genera are excellent at surviving and often flourishing in marginal environments.
