Government reports show wait times at Peel Health Campus during the first six months of 2019 have improved slightly - but the Mandurah hospital is consistently the worst performing of the three south metropolitan facilities.
The WA Department of Health collects data each month from 24 hospitals across the state, with Peel, Fiona Stanley and Rockingham General falling under the South Metropolitan Health Service.
All hospitals adhere to the four-hour rule, which was introduced in 2009, where medical staff look to treat emergency department patients within this time period.
The percentage of patients seen in four hours at Peel has been between 66.6 per cent (February) and 69.9 per cent (March) over the last six months.
For all six months, the percentage is higher than the equivalent period in 2018, meaning response times have improved.
However, Peel's performance was worse than Fiona Stanley and Rockingham in each of the six months.
Of WA's 24 recorded hospitals, Peel was in the bottom five for performance for each of the six months, with February's percentage the second worst in the state.
In terms of attendances, more people presented at Peel in five of the first six months of 2019, with 3788 patients in June the most.
The campus is operated by Ramsay Health Care. A company spokeswoman said the increased percentages were a sign of improvement.
"Despite extra demand caused by an unprecedented flu season, Peel Health Campus (PHC) has improved its Western Australian Emergency Access Target performance compared to the same time last year," she said.
"The hospital is continually reviewing its processes in an effort to improve performance.
"As a result has introduced a number of strategies, including the establishment of a new team-based model of care in the Emergency Department, improved practices around early discharge planning, which have resulted in PHC having one of the best "discharge by 10am" rates in the state.
"The hospital has also created some additional short-stay admission capacity, which is also helping with patient flow.
"Planning is now well underway for an upgraded ED that should assist with patient flow, enhance patient confidentiality and privacy, and improve overall patient comfort and satisfaction."
West Australian acting health minister Ben Wyatt said the state government had pledged $10 million to the Peel facility since their 2017 election win.
"The McGowan government care about the health needs of people in Peel so we have invested $10 million in Peel Health Campus, which includes a redeveloped Emergency Department," he said.
"During eight years in office the Liberal National government totally neglected the health needs of Peel residents and made no major investments in a hospital serving a growing, ageing population.
"Despite increased attendances caused by a severe and unprecedented flu season, Peel Health Campus has improved its performance - I thank the hardworking frontline staff for their efforts."