Oily-looking films are usually the most worrisome substances. The way to tell the difference between a bacterial film and oil floating on the water is to break the film. If the oily film stays broken, it is a natural bacterial film. If it flows back into place, it is petroleum, which indicates pollution. Collecting the bacteria and viewing them through a microscope is one way to tell important differences in the water chemistry from one site to the next.
Some bacteria thrive in near-neutral waters, and others thrive in acid waters.
Acid waters can be a result of mining activities. Looking at these microorganisms in the water is both a growing environmental field and an outdoors activity that can give hours of enjoyment. Techniques for collecting and studying the iron bacteria are simple and are presented here. These collecting techniques also work where the precipitate colors are different. Turquoise blue films may be made by bacteria that precipitate copper minerals.