Fish species are an important food resource all over the world, but the fishing practices of human beings are slowly driving many fish species to extinction. However, little is being done to communicate the problem of overfishing to the general public. In this three-part activity, students are introduced to the concepts of buoyancy and overfishing in an effort to provide a glimpse of how interesting fish are, and to raise awareness of overfishing. The students investigate buoyancy and gas compressibility by recreating a mysterious boat-sinking in the classroom, and by manipulating the buoyancy of artificial fish. By engaging in “fishing expeditions” with diminishing returns, the students learn why fish populations decline when we take too many of them. Throughout the activity, students have the opportunity to learn science as inquiry and the nature of science as presented in the National Science Education Standards.