Plankton:

These are microscopic plants and animal life that float in water and serve as a food for small sea creatures and fish. Generally, they are not injurious to health but they affect the taste of water by secreting oily liquid, which give bad taste and odour to water. Large quantities of plankton impart green, brown or yellow hue color to water. Due to their coloring tendencies, they may affect some industries like laundries, dye works, photographic paper etc.