Why are there so many American crayfish living in Japan’s wild environment?

I have traveled and toured the Japanese countryside and I have seen that crayfish live in ponds, rice fields, stagnant water, and drains, or cling to the drain walls. I admire how clean the water in Japan is, even drains, and creatures can live there.

But I just figured those crayfish are similar to the ones I saw in Louisiana, USA. Are they the same species? If so, why are they in Japan?