What's the correct way of saying "I went swimming this summer."?

[Fynriel]

Beginner here, so please don't judge me too harshly, but here's my pitch:

[ぼく は] ことし の なつ やすみ に うみ へ およぎ に いきました。
[Boku wa] kotoshi no natsu yasumi (ni?) umi e oyogi ni ikimashita.

Assuming I got the general idea down, I'm not sure whether I need a "ni" after the declaration of time here.

[community.japanese]

Fynriel san,
Konnichiwa.
That sentence is perfect!
Yes, you should put that ‘ni’ after natsuyasumi.
Yuki 由紀
Team JapanesePod101.com