That issue was cited in an on-line essay (interestingly enough) entitled NOTES ON THE GILL-MAN OF THE UPPER AMAZON,which talks about some lizard creature that apparently wandered through that particular issue of Cap.
The quote from below is from the article cited.
1976- While in a running battle with South American prison warden Hector "the Swine" Santiago, Steve Rogers, aka Captain America, runs afoul of the Gill-Man. The amphibious being eventually slays Santiago and his guards. ("The River of Death!" by Jack Kirby, Captain America #208, April, 1977.) In an attempt to make the Gill-Man look like a "new" monster, Kirby draws him with bulbous eyes and bright red scales. [The Marvel Universe is not the same as the Wold-Newton Universe, so presumably a mainstream Marvel title like Cap should be excluded. However, artist/writer Kirby has known Cap/Rogers since 1941, and in the Newtoniverse Cap sometimes opens his files to comic book legend Kirby. In fact, a letter from Robert Sodaro in this very issue states: "Since Jack started writing for Marvel again, the plotlines of CAPTAIN AMERICA. . . have had little if anything to do with the rest of the Marvel Universe."]The body of letter itself appears here:
It is really just one of numerous LOCs I got into print during those days, and well, I just thought I’d share.