Swimming or bathing in the sea; going to the seaside to swim and play in the ocean, typically a summer activity.
夏休みに家族で海水浴に行く予定だ。
We're planning to go to the beach for a swim with the family during summer vacation.
この海岸は海水浴場として整備されている。
This coast is maintained as a bathing beach.
海水浴の前には日焼け止めを塗っておいた方がいい。
You should put on sunscreen before going for a swim in the sea.