Consider this:
You have a farm. Cows, chickens, sheep, etc. One day you notice some of your cows have turned pink.
You decide to investigate. Is it an indicator or something else going on on your farm? Obviously it's a sign of something amiss. Perhaps in the grass they eat, or on the soil, or from the other animals.
In this lesson, we'll look at how physical and biological indicators of water systems reflect changes in these systems. In our example, the cows were our indicator that there had