For water monitors, pH is the measure of acids and bases dissolved in the water of a stream or lake. The range of the pH scale goes from 1 to 14. A measure of 7 is neutral. Any substance measuring higher than 7 is a base and anything below 7 is an acid. Common forms of acids are lemon juice, soda, vinegar, and acid rain. Common forms of bases are drain cleaner, ammonia, and baking soda. See the chart below to find the pH values of common substances.
Pure water, which is neutral, has a pH of 7. Substances dissolved in water form either an acidic or a basic solution. Waterbodies naturally become mildly acidic or basic depending on the rocks and minerals in the riverbank and watershed. A waterbody with a pH outside of the 6.5-8.6 range is unable to support a diverse amount of fish and invertebrate species. In the Northeast U.S., acidic waterbodies are more common and problematic due to the natural geology and influences of acid rain.