Why is it important to monitor pH levels in natural bodies of water?

Since pH can be affected by chemicals in the water, pH is an important indicator of water that is changing chemically

Explanation:

pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water. Water that has more free hydrogen ions is acidic, whereas water that has more free hydroxyl ions is basic

So the water is safe to drink, or so the aquatic life doesn't die