What is it?

The pH measurement shows how acidic or basic a water body is. The amount of hydrogen ion activity in water determines the level of pH on a scale from 0-14. The lower the pH value, the more acidic the water is. The pH range for natural bodies of The water in the United States is around 6.5-8.5.

Why do we measure it?

The pH is an important water quality parameter. Aquatic animals and plants are adapted to a certain pH range, but most prefer between 6.5-8.0. An increase or decrease in pH outside the normal range of a water body can be detrimental to organisms depending on their sensitivity.

A chart listing the effects of pH value. The chart ranges from pH 0, which is highly acidic, to pH 14, highly basic. The chart has examples of each pH value. 0: Battery acid. 1: Sulfuric acid. 2: Lemon juice or vinegar. 3: Orange juice or soda. 4: Acid rain (which has a pH value between 4.2 and 4.4) and Acidic lake (pH value 4.5). 5: Bananas (pH 5.0 to 5.3) or Clean rain (pH 5.6). 6: Healthy lake (pH 6.5) or Milk (pH 6.5 to 6.8). 7: Pure water. 8: Sea water or Eggs. 9L Baking soda. 10: Milk of Magnesia. 11: Ammonia. 12: Soapy water. 13: Bleach. 14: Liquid Drain Cleaner. The effects are listed as followed: at pH 4.2, all fish die; at pH 5.5 Frog eggs, radpoles, crayfish and mayflies die, and at pH 6.0, Rainbow trout begin to die.

Source: US EPA


What affects it?

A variety of natural and human factors can influence the pH level of a body of water. For example, water can be made more acidic by acid rain or the vegetation found near the water. The acidity of a lake or pond also depends upon its age. Older bodies of water typically have more organic material, which leads to lower pH levels as the organic material decays. Regardless of which end of the spectrum a pH level may gravitate toward, extremes in the pH level can be damaging to most aquatic organisms.

A chart showing pH ranges that support aquatic life. Bacteria survive from pH 1 to 13. Plants survive from approximately pH 6.5 to 9.5. Carp, suckers, catfish, and some insects from pH 6 to approximately 9.5. Bass, bluegill, and crappie survive from approximately pH 6.25 to 9. Snails, clams, and mussels survive from pH 7 to approximately 9.75. The largest variety of animals (Trout, mayfly/stone fly nymphs, caddisfly larvae) survive from pH 7 to 9. 
 Source: Michigan Sea Grant



Download Factsheet


 Login | This program is part of a cooperative agreement between the U.S. EPA Great Lakes National Program Office and National Oceanic Atmospheric Administration (through Illinois-Indiana Sea Grant) and funded by a Great Lakes Restoration Initiative grant: DW92329201. This website was developed by Illinois-Indiana Sea Grant and designed by Gabriel Horton. For questions or comments, please contact Kristin TePas at or 312-886-6224.