Salmon and trout are especially at risk at this time. Fish die-offs in shallow, warm ponds are fairly common occurrences during the summer. They will understand that warmer water holds less oxygen for fish, while cooler water holds more. Depending on what lessons they have already done and understood, make the connection between colder water and its ability to hold more oxygen. Have them make careful observations, writing them down if you wish.
Students can also record the water s temperature.
Discuss what they see and observe. Students should notice and mention the gills, fins, and the fact that the fish were opening and closing their mouths. Accept any logical answer. Before you do this next step, explain to students that the fish will be given warmer water to swim in, and since they are very hardy fish they can adjust to this. This is not cruel to goldfish.