National Koi Day is observed worldwide every July 7, celebrating the fascinating koi fish, which are colored varieties of carp originally from Japan. The holiday honors the legacy of Hanako, a scarlet koi believed to have lived for over 200 years, who died on this date in 1977. The systematic breeding of koi began in the 1820s in Niigata Prefecture, where farmers initially bred them for food before developing various ornamental colors and patterns. Today, there are more than a hundred koi varieties, classified into 16 groups, with the major ones including Kōhaku, Showa, and Sanke, collectively known as the Big Three. To celebrate National Koi Day, people can learn about koi fish and their symbolism in Japanese culture, visit local koi ponds or farms, watch related videos, and share pictures of koi on social media using the hashtag #NationalKoiDay.