Most of these are authored by what appear to be non-native English speakers. So, the most likely explanation is a translation issue.
In engineering literature from Russia from the 1960s, one sometimes finds references to a ‘water goat’ in papers that are otherwise about heavy machinery. It turns out this is a twice-translated rendition of ‘hydraulic ram’.
> engineering literature from Russia from the 1960s, one sometimes finds references to a ‘water goat’
Oh, that's where it comes from!
My dad told me something close when I was a kid, but according to him it was the early EU doing dictionary translation between English and French and getting "water sheep". I never could find it.
Through an unrelated anecdote, in my head this is now bound to the music of "smoke on the water", with a sheep impression for the guitar (bass?) — "Sheep on the water, ba baa baaah, ba ba ba baaah"
Hey, it's not that easy to chose between "водяной баран" and "гидравлический таран", you know.
My favourite example of troubled blind translation is still "naked conductor runs under the carriage".
That's on par with this (apocryphal) translation of "The spirit is willing but the flesh is weak" <=> "The vodka was good, but the meat was rotten."