Regarded as one of the best swimmers of his day, Karri Käyhkö won almost 30 Finnish titles along with an indoor water polo championship during his career. Käyhkö was an excellent freestyle swimmer, setting multiple national records, in addition to becoming the second Finn to swim the 100 metres freestyle in under one minute. At the Nordic Championships he won three titles in the 400 metres freestyle (1955, 1957, 1959), along with the 100 metres freestyle and the 4 x 100 metres medley relay titles in 1957. In the late 1950s he moved to the United States to study at the University of Michigan, where he also prepared for the 1956 Melbourne Olympics. Käyhkö had his best performance at the Olympics four years later when he came ninth in the 100 metres freestyle and fifth in the 4 × 200 metres freestyle relay at the Roma Games.