Is it a slang term of some kind?
edit: I do not know the etymology of the Swedish word for entrails, but I'd wager it's just coincidence that it is seemingly made up of two other words. It's not unlike the English word "searing" seemingly being composed of "sea" and "ring".
Just as you can't actually say inriver and pretend it means something in the river in English, you can't say inälv and mean something in an älv in Swedish. But as a pun it is okay, everyone gets the word play.
I think "in-river" is pretty acceptable in speech, and mildly so in writing. If you said there was an "in-river pool", I wouldn't bat an eyelash.
That said, the relation between the adjectivizing(?) morphemes "in-" and "at-" (e.g. "at-home bar") and their corresponding prepositions is weird and makes my brain hurt.
A Korean word "inbun", when followed by a number, means "amount of serving". So "3 inbun" means "serves three", or "a dish for three".
When NOT followed by a number, it is a different word (with exactly the same spelling and sound). It means "human feces".
[1] LOL, not really.
I have no idea what your second sentence is talking about. :/
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As expected, most of the names which received a lot of votes were silly puns and, you know what? They did accept the winning entry. Which means the pool is officially named "Pöl Harbor" ("Pöl" meaning puddle in Swedish). I myself was very pleased with this, though I was unsure whether I preferred this name or the rather gruesome runner-up: "Inälvsbadet". This literally means "the entrails bath", though the word for entrails could also be interpreted as "in-river", hence the pun.