The Jurien Bay Boat Harbour (JBBH) has experienced seasonal water quality issues that are mostly caused by seagrass accumulating and decomposing in the harbour waters.
Following extensive data collection, trials, modelling and studies, the Department of Transport and Major Infrastructure (DTMI) has determined reconfiguring the boat harbour entrance as the most effective solution to this issue.
The proposed entrance reconfiguration will consist of adding a 170-metre breakwater extension to the harbour’s northern breakwater.
DTMI also conducts maintenance dredging at the boat harbour (approximately every 2 years) to remove accumulated marine sand and seagrass.
Project background
JBBH experiences seasonal water quality issues that are mostly caused by seagrass accumulating and decomposing in the boat harbour.
The decomposing seagrass reduces oxygen in the harbour water and creates a strong hydrogen sulphide odour and occasionally results in the death of a large number of fish. These issues usually occur in winter through to spring.
Over the past decade, DTMI has completed a comprehensive data collection and research program to better understand these events and develop an effective solution.
This program included coastal modelling and environmental studies, data collection, and several trials including:
- dredging
- trawling, and
- use of a bubble curtain to prevent seagrass entering the harbour and to oxygenate the water.
Modelling studies showed that adding a 170-metre breakwater extension to the northern breakwater would divert a large amount of seagrass from entering the harbour, significantly improving the water quality.
The works will involve using trucks and earthmoving equipment to import and place rocks to construct the spur groyne.
This proposed structural modification may result in some periodic trapping of seagrass on the northern beach outside the harbour.
Project status
Project Update 18 September 2025
DTMI is currently monitoring the seaweed build up within the entrance channel at Jurien Bay Boat Harbour, and in the facility.
It was announced as part of the 2024-25 State Budget that the northern breakwater at Jurien Bay Boat Harbour is to be extended by 170 metres.
Dredging works are planned in late 2025, to remove the seaweed and deepen navigation channels, assist navigation, improve water quality and restore natural tidal flushing.
This follows thorough scientific investigation to determine the best way to remedy the annual accumulation of seagrass wrack in the harbour which has resulted in poor water quality issues, fish kills and beach closures.
Modelling studies show the reconfiguration of the harbour entrance will divert approximately 80 per cent of the wrack movement into the harbour, limiting potential for decomposition and deoxygenation of the water.
The reconfiguration project is now underway, with detailed design in progress and a request for tenders for the construction to follow.
The reconfiguration is expected to reduce the frequency of maintenance dredging and stimulate private investment through a leasehold development within the harbour.
JBBH maintenance dredging campaigns
DTMI completes maintenance dredging campaigns at JBBH approximately every 2-3 years.
Maintenance dredging is the process undertaken to remove accumulated marine sand and seaweed to:
- restore navigable depths for vessels;
- provide ongoing access and operational use of the harbour
- remove decomposing seaweed and maintain harbour water quality; and,
- restore natural tidal flushing.
Offshore placement
For maintenance dredging campaigns completed prior to 2020, dredged material has been placed onshore in a designated area north of the harbour.
As a more sustainable solution, DTMI is now returning the dredged material offshore into a natural seabed depression.
DTMI has secured environmental approvals for this offshore disposal location and the dredged material will be placed in this area during future maintenance dredging campaigns.
Maintenance dredging campaigns will be monitored and managed as per environmental approval conditions and the Jurien Bay Boat Harbour Maintenance Dredging Long Term Monitoring and Management Plan.
Offshore disposal location
