They found no trace of a mythical sea monster, no sign of mobsters in cement shoes or long-lost treasure chests. The dozens of dives that concluded this week were part of a first-of-its-kind effort to learn more about the source and potential harm caused by plastics and other pollutants in the storied alpine lake on the California-Nevada line. It's also taken organizers on a journey through the history, folklore and development of the lake atop the Sierra Nevada that holds enough water to cover all of California 14 inches (36 centimeters) deep.