The man known to the natives of the Amazon Jungle simply as Gringo (Stuart Whitman) is taking an excursion down the river in search of treasure, a journey he has undertaken before, but with disastrous results as he was the sole survivor of the party. Mind you, even when he is dozing on the upper deck, he is not quite safe as a tribesman tries to steal from him, but Gringo springs into action and cuts off one of the man's fingers, then to add insult to injury throws him overboard, forgetting that there are crocodiles down there...
Which is essentially an excuse to have a hapless extra fed to the reptiles in the first five minutes, a example of the sensationalist lengths director and co-writer René Cardona Jr would go to for his thrills. What Treasure of the Amazon closely resembled was a Mexican version of one of those unsavoury jungle adventures that brought the world the likes of Cannibal Holocaust, although Cardona never went as far as that, nor was he as pretentious as this was strictly a straight ahead storyline in an exotic setting. This in spite of informing us at the beginning we were about to watch a "true story", if you can believe it.
There were actually three straight ahead storylines to contend with, following Gringo and his untrustworthy band of unlovely criminals out to get their hands on the diamonds, and also a group of Americans led by Bradford Dillman (who has a penchant for rear-ending eagles with his plane) who find some gemstones in an old grave and think they can finally get their ticket out of this place if they can uncover more. Then there's the oddest explorers, a couple made up of ageing Nazi Donald Pleasence and his topless throughout the whole movie ally, Marimbo (Sonia Infante), who you might expect to be having some kind of showdown with the other two groups.
Well, you might expect that, but as it plays out Pleasence's Klaus, who hopes to reignite the Third Reich by himself (!), has almost nothing to do with the rest of the film, and seems to have been included to bump up the running time, for a star name to add recognition value, and so we can admire his companion in her constant state of undress. He does carry a machine gun, which you would rightly surmise he will use on the headhunters who plague everyone in this, frequently decapitating characters with unconvincing rubber bonce effects. Needless to say, scenes like these provide the most entertainment for the bad movie buff.
Also evidence of a lower budget than they might have liked is the way this is padded out with animal footage: honestly, you would have thought every creature in the jungle made an appearance in this, both great and small, leaving you with the impression that what Cardona really wanted to create was a nature documentary but did not have access to the services of David Attenborough. For what should have been a basically plotted tale that went from A (characters look for diamonds) to B (characters find diamonds and get the hell out) the sense of the production rambling lackadaisically through the motions never left it, and while there were some easy laughs to be had, none of them intentional, they were not quite enough to sustain what didn't half go on. Ridiculous highlights included an all-in wrestling bout between painted lady natives, supposedly a ritual but looking more like a brawl, and a victim being eaten by tiny crabs, but there were more consistent bad movies out there. Music by Mort Garson.