Background
The Department of Water and Environmental Regulation has responded to several reports of algal and water quality events at Ocean Reef and Mullaloo beaches since January 2024.
Following the collection and analysis of samples by DWER's phytoplankton ecology laboratory, only one algal event in January 2024 has been confirmed to involve a potentially harmful algae species which resulted in the beach being temporarily closed. DWER analysis of samples collected in the January 2024 event determined that the substance was likely to have been the naturally occurring algae Trichodesmium. Trichodesmium may be naturally present in the marine environment but may increase and become a visible event when particular conditions occur, such as a combination of calm and warm water temperatures.
The other algal events have involved natural marine floating debris with detections of naturally occurring non-harmful algae species.
On 14 March 2024, DWER responded to a report of a visible discolouration within the marine environment with subsequent investigations identifying a source of sediment entering the marine environment. This source has subsequently been rectified.
What's happening now
On 25 March 2024, DWER carried out detailed water quality sampling, at on-shore and off-shore locations around Mullaloo Beach and Ocean Reef. This included sampling from around the Beenyup Wastewater Treatment Plant water release point as well as background samples from the adjoining Marmion Marine Park. The samples were tested for more than 60 individual parameters, including metals, suspended solids, nutrients, algae, and pathogens. Samples taken earlier in March were also tested for hydrocarbons and organic substances. See map below of relevant sampling locations.
Results of analysis from laboratory testing has shown that:
- Chemical and metal levels are within the normal range for marine water. In particular, fluoride concentrations, which can be a marker for sewage effluent discharges, were not elevated.
- No hydrocarbons were detected.
- None of the algae species identified in the samples are known to contribute to contact irritation. While one species of concern (Pseudonitzschia seriata group) was identified, it was only in one off-shore sample location near the ocean outfall and this species is only potentially harmful to humans if they ingest affected shellfish.
- Levels of suspended solids (for example sediment or seagrass particles) around Ocean Reef and the north end of Mullaloo beach were elevated compared to other sample locations. Levels reduced in a southerly direction down Mullaloo beach. Future sampling and testing will assess any suspended solids to determine their content and potential source.
- There are no health concerns associated with these findings.
Suspended solids results
| Parameter | Background | S1.1 | S2 | S3 | S4 | S5 | S6 | S7 | Comments |
| Suspended solids mg/L | <5 | 148 | 164 | 171 | 49 | 77 | 36 | 34 | Offshore results range from <5 to 26 |
Results of the algae analyses have been shared with the Department of Health and the Department of Biodiversity, Conservation and Attractions and the City of Joondalup for their review and consideration as agencies responsible for health, the marine environment, and fisheries.
Maps of sample locations
Map 1
Map 2
Further investigations
DWER is engaging an independent and suitably qualified consultant to undertake an investigation of marine water quality within the Mullaloo beach area and the surrounding marine environment. The objective of the investigation will be 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 will include engagement with the local community to understand their concerns and observations in relation to local water quality.
Further updates will continue to be provided on this page as these investigations continue. Additional information on marine algae can be accessed via the Algal Bloom information page.
Current actions
DWER is aware of reports of Trichodesmium (sea sawdust) which have been reported on 24 April 2024 at Safety Bay, Point Perron and North Fremantle. The algae Trichodesmium has been confirmed by DWER's phytoplankton ecology laboratory to be present in samples collected by local government from the Rockingham/Kwinana areas. The algae Trichodesmium is not generally considered toxic or harmful to humans. DWER officers are attending Mullaloo beach to determine whether any algal blooms are present within this area and will undertake water quality sampling to verify marine water conditions.
You can view more information in the WA Health media release.
