There is an image of this
cultivar on the
Hosta Library. From the photo on the HL website, it appears to be a
size hosta with narrow, wavy, shiny green leaves and
creamy yellow streaked variegation. This non-registered cultivar was
originated in Japan.
Mikiko Lockwood in an article on The Hosta Library titled,
A Little About Japanese Hosta Terms defines the term
-gawa or -kawa as river.