No more bizarre than Ent Rails (you know, railways for Tolkien Ents) is the same as entrails in English.
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.
> Just as you can't actually say inriver and pretend it means something in the river in English
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.
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.