Background: The purpose of the present study was to describe factor structures of swimmers for evaluating endurance. The second aim was to determine 5000m pool velocity (5000Vp) and 5000m open water swimming velocity (5000Vow). Material and Methods: The study sample was comprised of 14 swimmers who candidate for the Turkish Open Water National Team (age: 13.78 ± 1.21 years; height: 168.06 ± 6.67 m; body mass: 59.06 ± 7.99 kg). Anaerobic threshold, critical swimming speed, and 5000m swimming tests were measured in a pool setting and 5000m open water swimming test was measured in sea conditions. Results: Results of the factor analysis; the effect of 4 cardiorespiratory endurance factor classified as velocity and heart rate (HR), HR and lactate, exercise HR and exercise lactate was explained 89.16% in relation with 5000m open water swimming performance and under the first factor had the greatest factor weight and formed 48% of the total variance. Regression coefficients for 5000Vp and 5000Vow were found R2 = 0.94 and R2 = 0.79 respectively (p<0.05). Conclusions: These findings suggest the equations of prediction specified in the present study may provide trainers more appropriate for evaluating performance in juvenile swimmers.