There is an urgent need for research on the epidemiology of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing corona virus disease 2019 (COVID-19), as the transmissibility differs between settings and populations . Here we report on a questionnaire-based retrospective cohort study of the prevalence and transmission of SARS-CoV-2 among participants in swimming activities in Denmark in the last five months of 2020 during the COVID-19 pandemic . Eight of 162 swimming activities with a SARS-CoV-2 positive participant led to transmission to 23 other participants . Overall, the percentage of transmission episodes was 4.9% (competitive swimming 8.9% ; recreational swimming 1.3 %). Overall, the incidence rate of transmission was 19.5 participants per 100.000 pool activity hours (corresponding values : 43.5 and 4.7 for competitive and recreational swimming, respectively). Compliance with precautionary restrictions was highest regarding hand hygiene (98.1 %) and lowest in distancing personal sports bags (69.9 %). Due to low statistical power, the study showed no significant effect of restrictions . Insight into the risk of transmission of SARS-CoV-2 during indoor swimming is needed to estimate the efficiency of restrictive measures on this and other sports and leisure activities . Only when we know how the virus spreads through various settings, optimal strategies to handle the COVID-19 pandemic can be developed.