"I swim a lot in the summer."
You use ni to indicate a specific period of time. Wa is more general. It translates more like during (the period of) Summer it's more relaxed and general. Ni is more specific, so it translates more like IN Summer (specifically) - you'd use ni to indicate that you are specifically swimming a lot at Summertime. Duolingo didn't convey the difference between wa and ni very well at all.
I was also wondering about this. I understood たくさん to be relating to "a lot" of objects and よく to be relating to doing something "a lot" (often).
Can anyone confirm with confidence?
It is the case that よく means "often" and たくさん means "a lot" or "many", but it seems like たくさん can be used in place of よく when talking about the frequency of something. Whichever you use, you would definitely be understood in that situation. The reverse is not true, however. You can't use よく in place of たくさん when it is being used to describe quantity.
Pretty sure it should be に instead of は because summer is a period of time. The whole sentence should be 私は夏にたくさんおよぎます。With I (私) being the subject and so therefore marked with は.
I believe you can also combine the markers to make 夏 には たくさん泳ぎます。Which in English is essentially the same sentence (in the summer I swim a lot).
Yeah having は just makes it seem to me like it's saying the summer swims a lot...
The topic is summer and what you do in summer. So summer, the topic, is marked by は.
But for は wouldn't it be " as for summer, I swim a lot" which is close in translation to the given english translation? So you don't use に in this case..?
Not desu because desu means it is all by itself while ~masu is a verb ending. ~masu is not some stand alone word like desu - it is part of a verb and it shows the mood, voice and tense of a verb.