 The Environmental Agency (now Ministry of Environment) of Japan added it as a vulnerable species (IUCN category) to the Red Data List in 2000.It is thought that the causes of its decrease are corruption of water quality and the spread of the American crayfish "Pacifastacus leniusculus", which was imported in the 20th century and has steadily proliferated in northern Japan.Some suspect that this American crayfish carries some disease, such as the crayfish plague known in Europe, that eliminates endemic crayfish.