Femoroacetabular impingement (FAI) is a disorder that causes hip pain and disability in young patients, particularly athletes. Treading water leads to increased stress on the hip, the effects of which are poorly understood. In this study, we used MRI to identify the prevalence of FAI anatomy in elite aquatic athletes that tread water. The prevalence of cam FAI was higher than that previously reported for any other sport. This study demonstrates that synchronized swimmers and water polo athletes are at increased risk of cam FAI, more than other sports.