Nanigoto no fukaki omoi ni Izumigawa soko no tamamo to shizumihateken - Senzai Wakashu(English Translation & Meaning)

何事の深き思ひに泉川
底の玉藻と沈み果てけん

Roma-ji: Nanigoto no fukaki omoi ni Izumigawa soko no tamamo to shizumihateken
English Translation: What deep sorrow was it
that brought you down, to sink
in the Izumi River,
all the way to the bottom
like the jewel-weed below?
Meaning: What deep sorrow was it that made you sink to the bottom of the Izumi River, to lie there like the jewel-like water weeds?
Commentary: Book Nine Poems of Lament 596

Headnote: "Composed when a boy in Nara called Jijū threw himself into the Izumi River"
Composed when a boy in Nara known as Jijū threw himself into the Izumi River. What deep sorrow made you sink and vanish as jewel-weed at the bottom of the Izumi River, the poet asks. He imagines the deep trouble the boy, who ended his own young life, never told anyone, and mourns him by likening his lovely form to the weeds on the riverbed.
The author, "Bishop Hangen," was a monk of Kōfukuji in Nara who rose to bishop and later became superintendent of Kōfukuji.

First line, "nanigoto no": "of what matter."
Second line, "fukaki omoi ni": "because of deep sorrow," with "fukaki," "deep," associated with the "Izumi River" of the third line and the "bottom" of the fourth.
Third line, "Izumigawa": the old name of the Kizu River in Yamashiro, a poetic place.
Fourth line, "soko no tamamo to": "tamamo" is an elegant word for water weeds, likening the lovely form of the boy who sank.
Fifth line, "shizumihateken": "hate" is to do completely, and "ken" conjectures a past cause, "why did he sink away entirely?"
Author: Hangen
Source: Senzai Wakashu
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