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The concentration of hydrogen ions (pH) can affect the organisms that live in water.

Aquatic organisms have adapted over time to survive and reproduce in a relatively narrow range of hydrogen ion concentrations.  Some bacteria can withstand environments that have high hydrogen ion concentrations (pH = 2 or 3); other bacteria can live at very low hydrogen ion concentrations (pH = 12 or 13).  However, most fish can only survive and reproduce in a water that is not very acidic or basic, but is water that is "just right".  Most fish survive best in water that is close to "neutral" or, in terms of pH, at a pH between 6.5 and 8.2.  Immature stages of aquatic insects (mayfly nymphs, stonefly nymphs, caddis fly larvae), snails, tadpoles, and crayfish are also very sensitive to changes in hydrogen ion concentration and seem to reproduce and survive best under "neutral" conditions (pH = 6 to 8).  In water that is very acidic (low pH values), the concentration of heavy metals ions (copper, aluminum, etc.) increases and, this in turn, has negative effects on the health of aquatic organisms.  



In general, more acidic conditions tend to cause animals to become less excitable and, in extreme conditions, can lapse into a coma.  More basic conditions can lead to animals becoming hyper excitable (over excited). 

Click here to see how acid rain affects certain organisms, such as trout.

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