The girl and her friends found their way into Källbybadet in Lund just after midnight. Police were called to the leisure complex at 12.45am and officers found the girl floating in one of the pools.
Police tried to resuscitate the girl at the scene of the accident and ambulance personnel continued on the way to Lund hospital. But at 2am doctors pronounced her dead.
The girls friends, all aged 16-17, were found by the side of the pool in a state of shock. The emergency services called their parents and a crisis group was called in to help those affected.
It has not yet been established how the accident happened.