It is a pity that every summer a few people drown at the beach. In some cases, these people were good swimmers. So how did it happen? Riptide!

• 很遗憾,每年夏天总有一些人在海边溺毙,而这些溺水的人中有些是很会游泳的。那么这究竟是怎么发生的呢？是激潮在作祟！