A report commissioned by advocacy group Safety on Swan has found that water users at the popular Matilda Bay area would be at "serious risk" if a government plan to build a ferry terminal in the area goes ahead.
The state government has cited an analysis it had commissioned which showed Matilda Bay was the safest location for the ferry terminal with "adjustments".
Opponents want the terminal to be moved to another location down the foreshore, but the government does not agree.
The safety of swimmers and water sports enthusiasts at Perth's popular Matilda Bay has again been thrust into the spotlight as the state government sticks to its plans to build a ferry terminal at the spot, despite ongoing opposition.
Construction has yet to start on the Metronet project, which would connect ferry services from Matilda Bay and the southern suburb of Applecross to a floating pontoon at Elizabeth Quay.
But the contrasting views of the state government and opponents of the project have been laid bare in two reports they commissioned separately on the terminal.
The Western Australian Planning Commission (WAPC) approved the Matilda Bay site in December last year. A government-commissioned analysis found the area, across the road from the University of Western Australia, was the safest location for a ferry terminal.
The report said all water activities there could continue with "adjustments" that were still being finalised.
However, another commissioned report by advocacy group Safety on Swan found the project would put children, novice sailors and other water users at "serious risk" of injury or death from being hit by a ferry.
The group has long opposed the project, and hired Paul Chivers, a risk assessor and the founding director of Riskfacilitator, to conduct a review of Matilda Bay.
The review also looked into the site the group would prefer — an area further along the foreshore at the location of a now-closed restaurant known as JoJo's.
Mr Chivers's report found the government would not be able to mitigate what he said were serious risks for a high-frequency ferry service moving in and out of a busy recreational waterway.
He found people in the water would be too close to the ferries, putting their safety at a risk.
"The issue is introducing a high-frequency vessel into an already complex recreational system when an alternative location provides greater opportunity to separate those activities by design," Mr Chivers's report stated.
"Good risk management should favour designing out foreseeable conflict rather than relying on people to continually manage that conflict in real time."
Mr Chivers told the ABC there would be a much better and safer separation between ferries and people in the water at JoJo's.
Transport Minister Rita Saffioti disagreed.
Speaking on 102.5 ABC Perth, Ms Saffioti pointed to the government's analysis of the different possible sites based on environmental, operating, waterway safety and public transport use criteria.
She said Matilda Bay was the safest and best option.
The government's analysis found JoJo's had an "unacceptable safety risk" to windsurfers and kiteboarders due to the "informal" nature of the sports, and the ferry route would also cross over vessel traffic lanes in Melville Waters.
At Matilda Bay on the other hand, it found all water activities could continue with "adjustments", including a wide exclusion zone where the ferry could not go.
Other adjustments could include reducing ferry speeds in the bay, and building the jetty out to a length of 40 metres, so children and swimmers could still play and swim close to the shore.
"Any bit of infrastructure we deliver has risk attached to it. But the aim is to mitigate those risks," Ms Saffioti said.
In the government's analysis, JoJo's was also not suitable because it was further to walk to the UWA campus and because it was close to a marine park with seagrass, and next to a "bush forever" site.
But Mr Chivers said JoJo's was the safer spot and did not need extensive mitigation measures.
"The question for government is whether it is reasonable to choose a location that requires more active management of conflict when another location provides greater opportunity to separate that conflict by design," he said.