In 1986, Lake Nyos, a volcanic lake in Cameroon, released a huge amount of carbon dioxide gas, killing over 1,700 people in the surrounding area. This case study, developed for use in a limnology or aquatic biology course, explores that event, introducing students to concepts relating to lake formation, thermal stratification, and dissolved gases. Students interpret graphs showing temperature, dissolved oxygen, pH, and conductivity measurements for the lake, and then synthesize these different types of limnological data to solve the problem. (Contains 5 resources.)