"It's not safe to go swimming in the river" 或者 "It's not allowed to go swimming in the river" 都是可以表达 "也不能下河游泳" 的意思。
这两个句子的来源都是由 "go swimming" 和 "in the river" 组成的。"Go swimming" 是一个短语，表示 "去游泳" 的意思。"In the river" 是一个介词短语，表示 "在河里" 的意思。
一些英文例句及其中文翻译如下：
It's not safe to go swimming in the river because of the strong currents. (因为湍流很强，所以不能下河游泳。)
The signs at the riverbank say it's not allowed to go swimming in the river. (河岸的警告标志上说不能下河游泳。)
My parents told me not to go swimming in the river because it's dirty. (我的父母告诉我不能下河游泳，因为河水很不干净。)