Swimming and Running present two different excercise modalities!
Swimming and running present two very different exercise modalities in terms of biomechanics, energy expenditure, and stresses, not to mention that they occur in two very unique environments. However that hasn't prevented humans from becoming particularly adept at both of these activities, which makes sense given the geographic distribution of human populations, think of it as either running or swimming to get to something or to get away from something else.