The pair had only just met each other that evening at a bar and had been drinking heavily, according to a report on the ORF website.
At some point during the evening they decided to go swimming in Gmunden, Upper Austria. Police said that the woman probably went into shock and struggled to breathe as the water temperature was so cold. The amount of alcohol she had drunk made it harder to regulate her body temperature.
Her body was discovered on Sunday morning.
The 20-year-old man who had been with her told police that she “had suddenly disappeared” but that instead of calling for help he had gone home. Police said he would face charges for failing to help her but that an autopsy had ruled out any foul play.