在海边游泳很好玩。
Swimming at the beach is a lot of fun.
可以改成这样吗?
Swimming is a lot of fun in the beach.
Swimming in the beach is a lot of fun.
其实为什么是at the beach而不可以是in the beach呢?
在沙滩不说in the beach,常说on the beach,很少说at the beach。
你的翻译法是中式思维,英语应该使用以it做形式主语的句型:
It is (much)fun to swim on the beach.
很多乐趣 的翻译是 much fun!