穿过海用Swim across还是swim though?

请先看across与through的区别
through表示“贯通、直穿、透过、穿过”的意思,即是从一头（边）贯穿到另一头（边）.
例The river runs through our city.这条河流经我们市.
He passed through the hall.他穿过大厅
across表示“横穿、横过、横渡、横跨”
例：I swam across the Changjiang River 20 years ago.
20年前我横渡了长江.
Look left and right before you go across the street.
过马路时要左右看.
所以用swim across the sea