Background
Over summer 2023–2024, the department investigated several reports of algae and water quality issues at Ocean Reef and Mullaloo beaches.
Only one event in January 2024 involved a potentially harmful algae, Trichodesmium (also known as "sea sawdust"). This algae is naturally occurring and can become visible under calm, warm conditions. The beach was temporarily closed as a precaution.
Other events involved harmless natural debris and non-toxic algae.
Key incidents and testing:
On 14 March 2024, a water discoloration was traced to sediment entering the ocean. This issue has since been fixed.
On 25 March 2024, the department carried out extensive water testing at onshore and offshore sites, including near the Beenyup Wastewater Treatment Plant and within Marmion Marine Park. Test results found that:
- Chemical and metal levels were normal. Fluoride levels, a marker for sewage, were not elevated.
- No hydrocarbons were found.
- None of the algae species identified in the samples are known to contribute to contact irritation. One species, Pseudo-nitzschia seriata, was found offshore near the outfall, but it only poses a risk if contaminated shellfish are eaten.
- Suspended solids (like sediment and seagrass) were higher at Ocean Reef and northern Mullaloo but decreased toward the south.
- There are no health concerns from these findings.
The test results were shared with relevant health and environmental agencies for their review.
Further investigations
In August 2024, the department engaged an independent and suitably qualified consultant, O2Marine, to undertake an investigation of marine water quality within the Mullaloo beach area and the surrounding marine environment.
The objective of the investigation was to assess marine water quality and identify whether there are factors in the area which may be contributing to either a reduction in water quality or an increased risk of pollution or algal events.
The investigation scope included engagement with the local community to understand their concerns and observations in relation to local water quality. The department would like to thank the community and other stakeholders for their input into the investigation. Local knowledge and input were critical to ensure the investigation addressed the concerns of the community.
Community forum 2025
The department is holding a Community Forum on Thursday 27 November at 5.30pm on the Mullaloo Water Quality Investigation.
This forum follows the previous community session held in August 2024 and provides an opportunity to hear directly from independent consultants, O2 Marine on the investigation and findings.
Professor Pattiaratchi from the University of Western Australia will also present on his studies and involvement in current activities relating to algal blooms in Western Australia.
If you would like to attend the forum, please email the AssuranceExecutive@dwer.wa.gov by 12 noon on Wednesday 26 November.
What's happening now
Show moreAn Investigation Report has been prepared by the independent consultant.
The full technical report is available through the publications link below as well as a non-technical short summary report.
In summary, the investigation determined that dispersion/dilution of treated wastewater from the Beenyup Outfall has not been substantially changed since the construction of the Ocean Reef Marina. The investigation showed no evidence that the Beenyup Outfall is affecting water quality at Mullaloo Beach. The introduction of the revised Ocean Reef Marina has reduced ocean current speeds close to the marina during typical summer and winter conditions, with further studies recommended.
Independent peer review
The department also commissioned an independent peer review of the O2Marine investigation. The peer review confirmed that the modelling tools used were suitable and accord with best practice. The peer review also validated key modelling approaches and conclusions in the report but made some recommendations for further studies including additional analysis and modelling to support the findings of the investigation.
The further studies are currently being scoped out and the work will be undertaken in the coming months to address the recommendations of the peer review.
The peer review report is available through the publiactions link below.
Frequently asked questions (FAQ)
Find answers to some frequently asked questions about the investigation approach and its findings, the peer review and further studies.
Further information
Show moreCommunity members and residents are reminded that it is important to report any water quality issues at the time they are occurring by calling the Environment WAtch Hotline on 1300 784 782 or using the online reporting tool.
Additional information on marine algae can be accessed via the Algal blooms information page.
Information on the Department of Health water quality testing can be accessed via the Microbial water quality webpages.
Submit a report to Environment WAtch
Show moreWhen you submit a report to Environment WAtch, you will receive a response from us acknowledging your submission. We may contact you for further information.
Not all matters reported to Environment WAtch are managed by the department. For reports that relate to another local government or other State or Australian Government agency, we will forward the report to the relevant authority. Please note you may remain anonymous.
You can call our Environment WAtch hotline on 1300 784 782 or use the form below to submit your report.
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