One big development in swimming is the pool itself, back in the late 1800's swimmers jump from a boat and swim on the sea.
Fédération Internationale de Natation (FINA) was founded on 1908, giving to the sport rules and and organization to watch them.
Women were not allowed to swim until Stockolm, 1912.
The Olympic Games competitions prior to FINA had included a variety of unusual events such as underwater swimming (1900), 200m obstacle swimming (1900) and plunge for distance (1904). Prior to the London Olympics, where a 100m pool was used, the ocean (1896), the River Seine (1900), and a little lake in St. Louis, USA (1904), had been used as Olympic sites.
At the beginning of the 20th century, most swimming costumes were made of knitted woollen materials.
Lots of things have changed since then, but the scense of the sport.