The third Monday in July (originally July 20) is Marine Day. It was observed for the first time in 1996, after being declared a national holiday a year earlier. Japan now has 16 annual holidays.
July 20 was actually designated Marine Commemoration Day way back in June 1941 to mark the return of Emperor Meiji to the port of Yokohama in 1876 from a trip to northern Japan.
But it was not a national holiday, and so a number of ocean-related organizations got together in 1991 to seek a holiday for the sea. Thanks to strong public support for the idea, July 20 was finally declared a national holiday in 1995 after several years of debate in the National Diet.
Until then, there were no holidays in the months of June, July, and August. The Japanese public was happy to gain a day off in the summer months, but the kids were probably the happiest of all, since they could now start their summer vacation - which frequently starts on July 21 - one day earlier.