Stagnant water bacteria. Coloured scanning electron micrograph (SEM) of bacteria attached protozoan body in stagnant water. Numerous proteinaceous filaments extend from the bacteria. With no movement and aeration, stagnant water becomes a prime breeding ground for biofilms, or a collection of bacteria or fungi. Left untreated, stagnant water often becomes home for dangerous diseases and pathogens such as legionella, E. coli, nontuberculous mycobacteria and pseudomonas-related pneumonia Magnification: x6000 when printed at 10 centimetres wide.