An Etymological Dictionary of the German Language/Schwamm
Schwamm, n., ‘sponge, fungus,’ from the equiv. MidHG. swam (mm), swamp (b), m., OHG. swam (mm), swamb, m.; comp. Goth. swamms, ‘sponge,’ OIc. svǫppr, ‘‘sponge.’ Within these groups, which are very possibly connected together, we must distinguish three words, probably of different origin, of which the Goth. stems were swamma-, *swamba-, and *swampu-. In ModHG. the first two forms lave been united; to the second form Gr. σομφός (for σξο-), ‘spongy, loose, porous,’ is primit. allied; the first is formed from schwimmen.