"禁止在河里游泳"用英语可以说成"Swimming in the river is prohibited"。
"Prohibited"是英文中表示"禁止"的动词，来自拉丁语"prohibere"，意思是"阻止"、"禁止"。
例句：
Swimming in the river is prohibited due to pollution. (由于污染，禁止在河里游泳)
It is prohibited to swim in the river after dark. (在天黑以后禁止在河里游泳)
The sign says "Swimming prohibited" . (标志上写着"禁止游泳")