Some taste and odors are caused by mineral constituents in the water, e.g. excess chlorine and hydrogen sulfide. However the majority of taste and odor are the result of biologic activity. Spring turnover of lakes and algal blooms are responsible for Blue-green algae (Cyanobacterium), Green algae and diatoms that introduce filter clogging organisms that also foul anion exchange resins, degrade effluent quality of demineralized water, which also interfere with flocculation and sedimentation and produce toxic organic compounds (negatively charged colloid oils) that contribute to taste and odor in the finished water.
People involved in water treatment speak generally of an 'algae' problem. In fact, it is more accurate to use the term 'plankton'. This term includes all the micro-algae that under favorable conditions (the presence of ideal amounts of nutrients, heat, and sunlight in the environment) can undergo periods of explosive growth. It also includes animal plankton (zooplankton), which belong to a higher level in the food chain, as well as Actinomycetes. All these organisms are sized within a range of a few microns to a few millimeters.