A Class A river (一級水系, Ikkyū suikei) is a river classification in Japan designated by the River Law (河川法, Kasen Hō). It is applied to rivers and waterways deemed to be important to the economy of the nation as a whole, as well as those deemed important to the conservation of nature within Japan. There are currently 109 rivers with this designation.
It is administered by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT).
Class B river
The smaller, but important rivers are designated as Class B rivers (Japanese language: 二級水系), nominated and managed by the local governments at the prefecture level, but reported to and concurred by the central government.
References
Class A river Wikipedia(Text) CC BY-SA