The inspector of custodial services is worried about the departure of the management team at what was until recently WA's "most crowded and hardest" prison.
Neil Morgan said the Bandyup Women's Prison felt calmer and more settled when he inspected it last year compared to the 2011 to 2016 period when it was "in crisis".
The design capacity of the jail is 209 but in 2016 the inmate population exceeded 400 for the first time.
The inspector had already deemed conditions unhygienic, lacking privacy and "completely unacceptable" two years earlier, when it was housing as many as 290 women.
Some were forced to sleep on mattresses on the floor, often with their head next to a toilet.
Most remand prisoners are now held at Melaleuca Remand and Reintegration Facility, which helped bring the numbers down to about 230 at last year's inspection by Mr Morgan.
"The change in population numbers and profile had a profound effect," he said in his latest report, released on Tuesday.
"A new-found sense of stability was evident."
But not long after the inspection the management team "had all but dispersed" and their replacements appeared unfamiliar with an improvement program that had been running since mid-2016, Mr Morgan said.
"We are concerned that this loss of knowledge and disruption to the management team came at a time when Bandyup's future remained uncertain," he said.
WA's Acting Corrective Services commissioner Tony Hassall said the inspector's report provided a fresh perspective.
"It is pleasing to see the inspector recognises that Bandyup and women's imprisonment is in a significantly better state," Mr Hassall said.
Mr Morgan also said the conversion of Wandoo Reintegration Facility for young male offenders into an alcohol and drug treatment prison for women presented some positive opportunities for rehabilitation if done properly.
The facility is scheduled to open in the second half of this year.