classic waka stream

in the vast open sky
the moonlight falls so pure—
that the water below
which held its shining image
was the first of all to freeze

Meaning
Because the moonlight in the vast sky shines so purely, the water that held its reflection was the first to freeze.
Commentary
Book Six Winter Poems

In the cold air of winter, the moon appears clearer and its light more intense. The poem imagines that the water, reflecting that brilliant light, is frozen by it, as though the moon itself had brought the chill.

This is a poetic expression that attributes the freezing of water to the purity and sharpness of the moonlight.
Author
Unknown Poet
Source
Kokin Wakashu
Other