An apparently-unauthorized, painted version of this cover appears as the cover image on the non-comics German magazine Silber Grusel-Krimi #297 (May 27, 1980). It is credited to Mehmet Gülergün. (Per Martin O'Hearn at http://martinohearn.blogspot.com/2017/09/swipes-across-water.html)
Colors credit from the letters page of Swamp Thing (DC, 1972 series) #14 & 18 (the latter correcting the misattribution of the colors to Glynis Wein in the letters column of #16); letters credit from the letters page of Swamp Thing (DC, 1972 series) #22.
Letters from Craig Ledbetter, Arne McConnell, Mike Burton, Brian W. Prescott and Les Peterson.