"He swims like fish in the water."

Translation: Úszik mint hal a vízben.

[Arcaeca]

Okay, now I'm confused... when do you use and when do you not use olyan? Does olyan get omitted where "like" functions as an adverb?

[96314081311257]

You've probably figured this out already, but still.

Olyan & ilyen work as adjectives, while úgy & így work as adverbs. Here "like a fish" describes the way he swims, so it has an adverbial meaning, there you can use így, but not olyan. Therefore another possible translation is:

Úgy úszik, mint hal a vízben.

[fruzsi1117]

El van mint hal a vízben

[mindgrain]

Than it is 'elvan', in one word.

[SedatKlc]

when do we use olyan and when not?

[ElieElKhou1]

Should there be a comma between "Úszik" and the rest of the sentence? Because I feel like the construction comes from "Úgy úszik, mint ..."