The tiny burrowing Short-Tailed Rain Crayfish - ombrastacoides parvicaudatus - was first documented during surveys of the King River Valley in the '70s and '80s.

It had not been seen in decades until recently when it was discovered in flowing water during a Hydro Tasmania environmental survey.

It was found in in two creeks that run off the slops of Mount Lyell, near Queenstown, into Lake Burbury, which was formed in 1991 as part of the King Hydroelectric Scheme and is a known crayfish hotspot for several endemic species.

Crayfish expert Associate Professor Alastair Richardson helped to find six crayfish species during the environmental survey last year.

"So little is known about the short-tailed rain crayfish, it's been difficult to make a determination on its status when for many years we were not even sure it was a separate species," Professor Richardson said.

"But we knew their preferred habitat and remarkably, within just 10 minutes of mooring our boat at our very first target site we found our first specimen and we then later discovered a female carrying eggs, which is very encouraging."