The quality of the water in the world is being decreased by pollution. You can could determine pH with indicators and see if there is a variance. If so, the pH might be harming the aquatic life. You can determine the solubility and temperature of oxygen in the water. Oxygen-consuming creatures need the proper amount of oxygen in the water to survive.
Fish are cold-blooded animals.
Their body temperatures rise and fall with the surrounding water temperature. The fish's body temperature affects the fish's metabolism. If water temperature increases, fish body temperatures will also increase. Most fish can tolerate a pH range from 5 to 9 in lake or river water. The graph represents the temperature change that occurs when heat is added to water.