Volatile prisoners at overcrowded WA jail

A damning report into Perth's maximum security prison has criticised almost almost every aspect of its operation, saying inmates are highly stressed and volatile despite the best efforts of staff.

Inspector Neil Morgan says Casuarina has strayed from its purpose of rehabilitating long-term inmates and is "stretched at almost every point" with both infrastructure and resourcing failing to meet expectations.

Casuarina was the most crowded male prison in Western Australia last year, operating at 190 per cent of its 371-inmate design capacity, with numbers peaking at 950.

Mr Morgan warns the prison has broken international conventions by mixing remand and sentenced prisoners and housing them in shared cells.

Inmates have become increasingly stressed and volatile, with the number on remand routinely rising to 40 per cent of the population and services being redirected away from long-term inmates.

Remand prisoners are "less settled and have higher rates of physical health, mental health and substance abuse problems", Mr Morgan said.

Overcrowding was so severe last year a toilet was used as an overflow holding area for protected prisoners.

Mr Morgan also said the prison's health professionals were understaffed and the facilities did not meet either the physical, mental or dental health care needs of its inmates.

And prisoners lacked employment, education, training and rehabilitation programs.

WA Prison Officers Union secretary John Welch warned the situation could threaten staff safety.

Inmates could "become bored and restless and this can sometimes lead to them lashing out, particularly at staff", he said.

Opposition leader Mike Nahan said the former Liberal government had planned a new prison and done extensive work.

"It was going to be expensive but it was a very innovative approach, which to my knowledge has just been dropped," he told reporters on Thursday.

Mr Morgan said overcrowding had increased despite a $640 million injection to expand prison capacity in 2010.

"History shows that if prisons are built, they will be filled."

The Department of Justice agreed a rising remand population had affected Casuarina's resources and therefore its performance, offender management and service delivery.

It said it shared concerns about prisoner welfare and had appointed an additional nurse and increased specialist psychological staff across metropolitan prisons.

More beds and maximising available resources were also being looked at, the department said.