pH and Water Quality
pH measures the acidity of the water. Thescale goes from 0 to 14 with 7 being neutral and numbers below 7 representing additional acidty and numbers above the lack of acid or "basic" conditions. Most organisms thrive in water that is near neutral.
As the amount of acidity increases, the impacts on aquatic life also increase. The acidity is toxic to aquatic life, contributes to the release of toxic metals into solution, and weakens the shells and skeletons of biota.
Major sources of acidity are industrial wastes and deposition of acids from air pollution (acid rain), The figure below shows some common items and their place on the pH scale. It also shows the levels at which various biota are impacted by acidity.