An Etymological Dictionary of the German Language/Annotated/Sumpf
Sumpf, masculine, ‘swamp, bog, marsh,’ from the equivalent Middle High German sumpf (wanting in Old High German, in which sumft is used). Corresponding to Dutch somp, and with an old gradation English swamp (dialectic sump). Old High German giswumft and Gothic swumfel, ‘pond,’ are differently derived. Its connection with schwimmen (Sumpf, ‘porous soil’?) is very dubious; it is preferable to connect it with Old Icelandic svǫppr, ‘sponge.’ The Teutonic root was probably swemp; English dialectic swanky, ‘marshy,’ may point to an originally swenq.