An Etymological Dictionary of the German Language/schwimmen
schwimmen, vb., ‘to swim,’ from the equiv. MidHG. swimmen, OHG. swimman; corresponding to the equiv. OSax. swimman, Du. zwemmen, AS. swimman, E. to swim; OIc. symja points to Goth. *sumjan (pret. swam). Akin also to Goth. swamms, ‘sponge,’ swumfsl, m., ‘pond.’ The Teut. root swëm, sū̆m, appears also in Sund; comp. also OIc. svamla, MidHG. swamen, ‘to swim.’ In the non-Teut. languages the root swem, sū̆mm, ‘to swim,’ has not yet been found.