The blue marron is a naturally occurring variation of the smooth marron, Cherax cainii. Typically the marron is brown, black, or even green. Marron are naturally found only in Western Australia, although they have been introduced to other parts of Australia as well. Marron are the third largest species of freshwater crayfish, the other two larger species are also found in Australia and Tasmania.
There are two species of marron, the smooth marron is Cherax cainii, and the hairy marron, Cherax tenuimanus. The hairy marron is found only in the Margaret River system. (See a picture here) Only recently have the two species been separated. Some people have referred to the Red Claw Crayfish (Cherax quadricarinatus) as the Queensland Marron, as it also gets quite large, but not quite as large as the marron.
Sometimes compared to a freshwater lobster, the smooth marron is farmed in Western Australia, where demand for these tasty crustaceans is high. Outside of Australia it's relatively unknown, which is unfortunate. Because they are raised in fresh water their meat is sweeter than other saltwater crustaceans.