BACKGROUND: Respiratory complications such as swimming-induced pulmonary edema (SIPE) are a common feature of United States Navy Special Warfare (NSW) training.RESEARCH QUESTION: This study was designed to evaluate the incidence and clinical features of SIPE seen in this population.STUDY DESIGN AND METHODS: A prospective, observational review of all NSW candidates over a 15-month period was designed. Baseline height, weight, and ECG data were obtained. Candidates with respiratory issues were evaluated with a two-view chest radiograph and ECG while symptomatic and were closely followed up. The chest radiograph and clinical data were then independently reviewed.RESULTS: A total of 2,117 NSW candidates participated in training during the study period, with 106 cases of SIPE identified (5.0%). Ten additional cases of SIPE were repeat episodes in candidates already diagnosed. Forty-four cases of pneumonia were identified (no repeat cases). The majority had cough (90.4%), frothy-pink sputum (35.6%), and hemoptysis (23.7%). Overall, 80.1%of candidates had an oxygen saturation≥ 90%. Physical examination findings were variable: crackles (50%), wheezing (36%), and rhonchi (19%). Several had more than one feature; 23%presented with a normal examination. Radiologic findings in patients with SIPE most commonly revealed an interstitial pattern with perifissural thickening, larger average azygos vein diameter, larger average heart size, and normal lung height. ECG findings were not significantly different from baseline. Height and weight were not significantly different between the groups. Lower water temperatures were suggestive of increased SIPE incidence, but this was not a statistically significant trend.INTERPRETATION: The burden of SIPE in NSW training was greater than anticipated. Clinical symptoms and physical examination assisted by imaging were able to differentiate SIPE from pneumonia. ECG was not a useful diagnostic or screening tool, and height and weight did not affect risk of SIPE.TRIAL REGISTRY: Institutional Review Board registration at Naval Medical Center, San Diego, California; Registration No.: NMCSD.2017.0020.