The pH is the measure of the acidity
of water. The pH in the stream will affect what types of organisms
can live in the stream.
The pH in a stream can change when water is polluted. For example,
air pollution from coal-fired power plants can cause acid rain.
When the acid rain finds its way into the stream the pH in the stream
See what happens when you adjust the pH by sliding the bar back
and forth on the image. Notice how some organisms cannot live when
the pH changes only slightly.