The prison muster topped a record 5000 this week for the first time in the State's history, prompting concerns about acute overcrowding, "disgraceful" conditions for women and bed expansions which could lead to higher rates of reoffending.
Former independent prisons watchdog Richard Harding has predicted that based on the increase over the past four years, the prison population will grow to 6400 by the next State election.
The estimate does not take into account law and order election promises, such as tougher three-strikes burglary laws, which will also add to the prison muster.
Writing for _The West Australian _today, Professor Harding says well-known problems causing the high rate of imprisonment are not being addressed amid a "policy drift" across the State Government.
Professor Harding said the remand rate for unconvicted prisoners was too high, there had been a disproportionate increase in female prisoners, conditions in the only jail for women had become "disgraceful" and extra beds had been created in the wrong security settings.
"The department's building priorities have not only distorted its ability to manage the population equitably, but almost certainly have cemented reoffending rates at a higher level," the former inspector of custodial services said.
A department spokesman said the muster reached 5004 on Monday morning but had reduced to 4991 at midnight on Tuesday.
He said the department had to accommodate everyone incarcerated by the courts.
"We do not have the option of putting up a 'no vacancies, we are full' sign," he said.
The prison system has an operational capacity of 5269 prisoners and a $655 million building program is almost complete.
The spokesman said moves to improve female facilities had begun.