A Hundred Verses from Old Japan (The Hyakunin-isshu), tr. by William N. Porter, , at sacred-texts.com
THE Mina stream comes tumbling down
From Mount Tsukuba's height;
Strong as my love, it leaps into
A pool as black as night
With overwhelming might.
It was a frequent custom in the old days for the Emperors of Japan to retire into the church or private life, when circumstances demanded it. The Emperor Yōzei, who was only nine years of age when he came to the throne, went out of his mind, and was forced by Mototsune Fujiwara to retire; he reigned A.D. 877-884, and did not die till the year 949. The verse was addressed to the Princess Tsuridono-no-Miko. Mount Tsukuba (2,925 feet high) and the River Mina are in the Province of Hitachi.
Koi here means the dark colour of the water from its depth, but it also means his love, and is to be understood both ways. Note also mine, a mountain peak, and Mina, the name of the river.