Swimming becomes an organized sport at the early of 19th century, at that time the national swimming society of Great Britain began to hold competition
The very first swimming Olympic event were freestyle or breaststrokes, it was added in 1904. they discovered that they could go faster by bringing both arms forward over their heads. So they decided to call it butterfly.
Long course pools (50 meters) in Olympic
Short course pools (25 meters) in FINA world