In swimming, mixed relay races were introduced at the 2014 FINA World Swimming Championships (25 m) (4 × 50 m freestyle and medley), the 2015 World Aquatics Championships (4 × 100 m freestyle and medley), and the 2020 Summer Olympics (4 × 100 m medley). In open water swimming, mixed-gendered relays were introduced at the 2011 World Aquatics Championships (4 × 1250 m).