Microbial ecology and water pollution, particulate suspended colloidal material in the water column of Lake Erie has been investigated on a physical, chemical, and biological basis. Various inorganic and detrital fractions have been characterized using differential and gradient centrifugation in conjunction with electron microscopy. The particulates are comprised of substances of varying densities and sizes; fractions exert in influence on growth and metabolism of microorganisms. Various pesticides are associated with these fractions, such as the chlorinated hydrocarbons, endrin, aldrin, heptachlor, and lindane. The significance of the involvement of such pesticides in the micro-ecology is great since it is now known that microbial cell yields, DNA, RNA, and protein patterns of synthesis are affected. These facts strongly suggest that presence of chlorinated hydrocarbons in water seriously alter microbial metabolism and in turn affect higher life forms in ways presently not understood. Experiments on removal of aldrin from lake water using flocculent bacteria showed that floc forming bacteria adsorbed and concentrated aldrin from a colloidal dispersion. The settling of the bacterial flocs removed the chemical from the water phase.