Otylia Jedrzejczak claimed the gold medal for Poland after a thrilling finish in the women's 200m butterfly.
The 20-year-old, who has already won two silver medals in Athens, pipped Australian Petria Thomas for gold in a time of two minutes 6.05 seconds.
Thomas, gold medallist in the 100m butterfly and the 100m freestyle relay, had gone out at world-record pace but tired in the final 50m.
Yoko Nakanishi of Japan took the bronze medal in 2:08.04.
Jedrzejczak is Poland's first Olympic swimming champion.
She won two silver medals within in an hour on Sunday when she finished second in both the 400m freestyle and the