What killed the fish?

In scenario 1, we noticed there was a huge amount of rainfall in August as well as a huge amount of pesticide in the river. Because we know that pesticides are harmful to fish we could rule out the other options of the fish kill. We came to the conclusion that the rainfall washed pesticides from farms near by into the river, causing the pesticide level to spike and kill the fish.

In scenario 2, we noticed that the water temperature was more than 10 degrees hotter than it had been in the past three years. Because we know that water temperature affects the dissolved oxygen and carbon levels, we decided to look into these to aspects of the fish kill. There was a raise in carbon level and a decrease in dissolved oxygen.  We concluded that the spike in these levels was caused by the increase in temperature, and therefore, killing the fish.