"Our father lets us swim in the sea."
Translation:Unser Vater erlaubt uns, im Meer zu schwimmen.
I disagree with this sentence (German is my mothertongue), nobody says "in dem Meer", we abbreviate this to "im Meer". In answer to other comments: yes "zu" is really necessary.
a 'sea' is not necessarily an 'ocean' - for instance the Red Sea wouldn't be described as an ocean.
It represents a change of subject, or the fact that the subject is missing from the second clause. The actor of "swimming" is "us", not "our father." Check out infinitive clauses: http://www.mein-deutschbuch.de/lernen.php?menu_id=49#infinitiv_mit_zu
Ist es richtig zu sagen: "Unser Vater lässt uns in der See schwimmen"? Ich dachte, dass sie waren synonyme -Die See und das Meer.
Das stimmt, aber "die See" (statt "der See") klingt eher gehoben (~poetic). Normalerweise ist es "das Meer".
In my opinion: sea = Meer (Scharzes..), See (Nordsee, Ostsee) ocean = Ozean Sea is not ocean.
I agree with previous commentators here. I don't think 'Sea' and 'Ocean' are interchangeable and I would be surprised if they were in German. Nobody talks about the Atlantic Sea, or the Baltic Ocean, so I don't think Duolingo should try to teach them as being synonymous.