You can see the same with the word "sea". Its German equivalent See still mainly means "lake", even though in some fixed expressions it can be translated as "sea" (e.g. Nordsee, Ostsee).
Yeah, my mother tongue is similar, "sea" and "ocean" has the exact same word, so of course when I speak English I accidentally call a bunch of seas for oceans instead.
I remember reading that, in middlelow German the meanings were swapped “See” meaning the ocean and “Meer” meaning large body of standing water.
That’s probably why the lake is called “Steinhuder Meer”.
In low German the word for ocean still is “See”.