Swimming (the activity or sport), i.e., the act of moving through water by using limbs.
毎週日曜日にプールで水泳の練習をしている。
I practice swimming at the pool every Sunday.
水泳は全身を使う良い運動だ。
Swimming is a good exercise that uses the whole body.
彼女は高校時代に水泳で全国大会に出場した。
She competed in the national swimming competition in high school.