Japanese street gutters are NOT this clean

While browsing the depths of the internet I came across images and articles about the clean gutters of Japan. Apparently they're so clean that koi spawn in their exceptionally clean waters. I explore this claim.
 

BEGIN Japanology - Nishikigoi

Koi (鯉]) or more specifically nishikigoi (錦鯉 , literally "brocaded carp"), are ornamental varieties of domesticated common carp (Cyprinus carpio) that are kept for decorative purposes in outdoor koi ponds or water gardens. Koi varieties are distinguished by coloration, patterning, and scalation. Some of the major colors are white, black, red, yellow, blue, and cream. The most popular category of koi is the Gosanke, which is made up of the Kohaku, Taisho Sanshoku, and Showa Sanshoku varieties.