It is 1956, 11 years after the war and Japan is, in some respects, still a poor and struggling country. On the other hand, Japan is also becoming relatively prosperous because of the Korean War. Near the mouth of the muddy Aji River in Osaka, there is a small riverbank restaurant run by Shimpei and his young second wife. His son, nine-year-old Nobuo, makes a new friend. Kiichi, a boy about the same age. He and his 11-year-old sister live on a houseboat, newly moored by the river, with their mother. Nobuo's parents do not discourage his new friendship; indeed, they invite Kiichi and his sister to the restaurant, but they tell Nobuo never to visit the houseboat at night. Naturally attracted to what is forbidden, Nobuo does not understand his parents' reasons but guesses it has something to do with his new friend's mother.

"Now that the Japanese cinema has definitely lost its post-war eminence, now that box-office greed rules and the standard product is violence, porno or mindless ephemera, now — indeed — that Kurosawa experiences the greatest difficulty in making a film and Mizoguchi and Ozu, were they alive, would not be allowed to make a film at all, it is a pleasure to welcome a film as honest, as sensitive, and as true as Muddy River.

"Though director Oguri was too young to have known post-war Japanese life, he obviously knows post-war Japanese films and he has in this work revived one of Japan's most important (and otherwise forgotten) film genres, the shomin-geki, that wonderful category of films about ordinary people and ordinary lives, as seen in the pictures of Shimazu, Naruse, Ozu, Gosho and many others of the finest of Japanese filmmakers. It was films like these, and films like Muddy River, which so beautifully showed Japanese life as it was (and is) and reflected that equally important acceptance of reality through which the Japanese audience enabled post-war cinema to reach its heights.

"It is fitting that Muddy River was made outside the industry (indeed, it could not have been made within it) because the only hope for Japanese cinema as a whole now lies with independent producers and directors. Director Oguri and producer Kimura took a very long chance in making a picture they wanted to make, and in completing it without any distribution possibilities. This kind of bravery is now necessary if Japanese film at its best, at its most honest, is to continue." Donald Richie.