Shiro and Marilyn (1988)

So strong is his love that he braves 2 miles of ocean to swim to the side of his beloved.

Based on a true story. Shiro, a dog who lives in an inn on Akajima in Okinawa, swims to the opposite shore on Zamami to see his love, a dog named Marilyn. Shiro is portrayed by the real-life Shiro.