The marbled crayfish was found as pet in Japanese aquarium trade. In 2006, Sapporo Salmon Museum (Sapporo City, Hokkaido) accepted the unknown crayfish from volunteer conservationists. They collected from a river from Sapporo City. As the crayfish show marble color patter on their carapace and their juvenile are all female, it identified as parthenogenetic Marmorkrebs.
The Google Map that I maintain of Marmorkrebs introductions has been updated accordingly.
Kawai T, Takahata M (eds.). 2010. Biology of Crayfish. Sapporo: Hokkaido University Press. 556 pgs. ISBN: 978-4-8329-8194-2.
Sapporo Salmon Museum picture from here.