High-level competitive swimming is a sport that presents high loads on the human organism. That is the reason we have to provide the body with adequate and sufficient nutrient input for successful activity. In addition to the consumed macronutrients and micronutrients, hydration is equally important. The assignment aimed to present the nutritional requirements of professional swimmers, with more emphasis on open water swimming. The eating strategy varies according to the intensity and duration of the exercise. Through the survey, we received an insight into the eating habits of Slovenian swimmers. It turned out that the majority (88 %) eat breakfast in the morning, most commonly food rich in carbohydrates. They represent the highest percentage of daily energy intake and are crucial to enable strenuous training and competitions. During exercise, 72 % of respondents maintain sufficient level of glycogen in the body with sports drinks, and for fast regeneration, more than half provide themselves with a high-quality meal as soon as possible after the workout is completed. Nutritional supplements should also have a potentially positive effect on achieving better results. The studies carried out have namely confirmed the beneficial effects of creatine and caffeine, components in dietary supplements.