You can sprint intervals, cycle in intervals, even incorporate resistance into your interval training. For those who want to try something new and different, a study published in the Journal of Sports and Conditioning Research looks at what you can achieve from interval training in an Olympic sized pool.
Scientists assigned 24 former competitive swimmers to swim freestyle intervals at 50 meter or 100 meter distances. The 50 meter swimmers did 12 to 16 bouts with 15 seconds of rest between each. The 100 meter swimmers did 6 to 8 bouts and got 30 seconds in between.
After 8 weeks of training, both interval distances improved 100 meter and 400 meter swimming performance with increased stroke length and greater maximal aerobic speed. There were no significant differences between groups, and 50 meter sprint times remained unchanged.