As the winter sun dipped behind the Rocky Mountains of Glacier National Park, Linnea Mills, 18, waded into the frigid, glass-clear waters of Lake McDonald, two hours north of Missoula, Montana. It was just after 5 P.M. on November 1, 2020. The air was crisp, the shoreline quiet, and fresh snow clung to the alpine peaks above.

Linnea was participating in a scuba dive certification class designed to introduce her to the technical demands of cold-water diving, including how to use a drysuit. Within an hour, the training exercise unraveled into a cascade of accidents.

She would not resurface alive.

Her death has since raised difficult questions about the hidden risks of diving in one of the country’s most iconic parks, and about the safety protocols that diving companies must follow. Linnea’s life, and the events that led to her accident, are presented in a new documentary, How to Kill a Mermaid: The Linnea Mills Story. The film explores the events surrounding her death using law enforcement body-camera footage and video from her final dive.

Outside’s Madison Dapcevich sat down with the filmmaker, Damon Ristau, and spoke with her brother and father to learn more about her death and its implications for the scuba-diving industry as a whole. Outside reached out to the dive instructor who was present during Linnea’s death, as well as the instructor’s attorney, but we did not receive a response by the time this story was published.