South East Queensland dams were built to high safety standards, but most were built some decades ago. Methodologies and data used to estimate extreme rainfall events continue to improve and industry engineering standards and understanding of risks can progress over time. 

Across Queensland and Australia, there are multiple dam upgrades occurring to meet modern engineering standards. 

Seqwater’s Dam Improvement Program is ensuring the region’s dams comply with the latest safety standards and continue to function safely during extreme weather events in line with regulatory requirements.  

Click here for more information on Seqwater’s DIP, including dam upgrades which have been delivered and currently under planning.

Lake Macdonald – also known as Six Mile Creek Dam – was originally constructed in 1965. 

There have been significant advances in dam design since the dam was built, as well as new ways of estimating extreme rainfall and flood events, and a greater understanding of the size and severity of earthquakes.

This will be the first major upgrade of the dam since the wall was raised in 1980. The Lake Macdonald Dam Improvement Project will:

•    increase the spillway capacity to safely pass floods 
•    protect the dam wall in extreme flood events
•    efficiently control water flowing out of the dam 
•    reduce risks to the dam structure during earthquakes
•    meet modern design and engineering standards
•    comply with dam safety guidelines.

The new dam will occupy the same footprint as the current structure, however the spillway will be a split-level concrete spillway. The primary ‘ogee’ spillway is set at the original lake level, and an upper labyrinth spillway will be constructed for large floods. No spillway gates are included in the new structure and the earth embankments will be reconstructed to their original level on either side of the primary spillway. 

The primary spillway is a flat concrete structure, similar to the current dam wall. 

The labyrinth spillway has a zigzag shape when viewed from above and is made from concrete. In the event of a very large inflow, the water will flow over the upper labyrinth spillway and into Six Mile Creek downstream.  

The current earth fill embankment on the Lake Macdonald Drive side of the spillway does not meet today’s design and safety standards – that is, it is too steep and at risk of erosion. The new embankment at this location will be the same size and height of the existing embankment and finished grass and rocks.

The right earth embankment on the other side of the dam's spillway, closest to the water treatment plant, will also be re-constructed and finished with grass (looking much the same as it does now).   

Rocks will be placed downstream of the new spillway, called scour protection, and will assist in preventing erosion.  

An outlet tower will be constructed to the left side of the spillway which will have mechanical pipework and electrical components to facilitate both emergency release of water, to lower the dam reservoir, and environmental flows to the downstream Six Mile Creek.

​Construction works are planned to begin from March 2025, subject to approvals and environment conditions. Works will take place between 6:30am and 6:30pm Monday to Friday, weather and construction conditions permitting. Working hours on Saturday are between 6:30am and 4:00pm, as needed.  

​The entire construction process, from building the cofferdam to its removal after the new dam wall is complete, is anticipated to take around five years, depending on weather and site conditions. 

Key activities will include:

• Vibratory piling 
• Concrete and rock breaking 
• Earthworks 
• Concrete pours 
• Rock filling. 

​Please note that the construction schedule is subject to change based on environmental and operational factors.

Construction of the Lake Macdonald Dam Improvement Project (DIP) will be delivered in four (4) phases and is expected to be completed in 2029, subject to weather and construction conditions. 

Construction phases and timeframes are as follows:

• Phase 1 (2025) – Construction of temporary cofferdam
• Phase 2 (2025-2026) – Demolition of existing dam wall
• Phase 3 (2026-2028) – Construction of new dam wall and infrastructure
• Phase 4 (2028-2029) – Remove cofferdam and site rehabilitation.

The Lake Macdonald Dam Improvement Project is a $427.7 million project to ensure ongoing dam safety and water security for years to come.

To maintain local water security during the construction of the project, a minimum Full Supply Volume of 42% will be retained for Lake Macdonald Dam (which equates to a level of 93m AHD), and the Noosa Water Treatment Plant will continue to operate. 

To the community, this will look approximately two metres lower than the dam's full supply level. 

This is the level the lake will remain throughout construction unless dry conditions create a naturally lower level.

All Seqwater dams within the Dam Improvement Program continue to operate safely. Dam improvements are undertaken to meet modern guidelines for these life-long assets – many of which were built some years ago. 

Seqwater undertakes regular monitoring and engineering assessments to ensure all our dams continue to operate safely. 

Dams in Queensland were built to high, internationally accepted safety standards. However, the methodologies and data used to estimate extreme weather events and flooding impacts have significantly improved, and engineering standards and risks have progressed. 

All these factors are considered as part of Seqwater’s Dam Improvement Program so our dams continue to operate as they should, now and into the future.

A 300 metre long, 10 metre wide temporary cofferdam structure is engineered to manage inflows after each rain event. This structure will hold back the water in Lake Macdonald during construction of the new dam wall.

This is a temporary measure for dam safety and once the new dam wall is complete, the cofferdam will be removed, and Lake Macdonald Dam will be able to naturally refill to its original full supply level.  

The cofferdam will be constructed from sheet piles, tie-bars, structural steel members, rock bags, and graded rock fill. Cranes equipped with vibratory and impact hammers will drive the sheet piles into place. The same cranes will be used to install the tie-bars, structural members, and rock bags. Rock fill will be delivered by trucks and positioned using earth-moving equipment.

The community can expect to see an increase in standard construction impacts intermittently throughout the project including noise, dust, vibration and increased heavy vehicle movements.

At times, out of hours work including weekend, night and continuous work will be required to complete time critical activities.

We will provide advance notification to the community and stakeholders prior to commencing any out of hours works.

We understand some activities will be more disruptive for residents in close proximity to the project, and will be in contact with those directly affected to advise of impacts and mitigation measures in advance.

Click to read our fact sheets for more information on traffic management, work hours, and noise, dust and vibration mitigation measures.

We thank the community in advance for your patience and understanding while these essential works are carried out. 

Lake Macdonald is expected to remain open to on-water recreation, and parks and facilities recreation throughout the project. This means Lake Macdonald, Lake Macdonald Park and the boat ramp along Lake Macdonald Drive will remain open, as well as the Noosa Botanic Gardens. Recreation activities including motorless boating, canoeing and fishing will be permitted outside of the construction zone, which the cofferdam will isolate.

There will be closures to the scouts campground, the Mary River Cod Park and boat ramp, the fishing platform on Lake Macdonald Drive and some walking, riding and horse trails.

The Noosa Trail Network will remain open, however access points to the trails may change during construction. Vehicle parking and foot access will be closed at the Lake Macdonald Drive trail head (near Kookaburra Park) and along Collwood Road due to construction activities. Plans to provide alternative access and vehicle parking for the Noosa Trails Network in this vicinity are being worked through with Noosa Shire Council.

During construction, the local community and stakeholders will see an increase in construction traffic, including heavy vehicles in and around Lake Macdonald.

Heavy vehicles are approved by the Office of the Coordinator-General to use Elm Street and Lake Macdonald Drive, and these will be the main areas with increased construction traffic.

A Traffic Management Plan has been developed to ensure the safety of residents, road users and construction workers during the project.

Temporary traffic changes will occur at different times and may include speed limit reductions, lane closures, temporary traffic signals, traffic controllers on site and temporary signage.

Fencing and barriers will also be installed to delineate safe work areas from public spaces.

We will provide advanced notifications to the community and stakeholders prior to any major traffic changes or diversions.

During construction there may be partial road closures and temporary changes to traffic conditions at times for the safety of road users.

We will provide advance notification of any road closures, including details of any detours.

We are working with qualified ecologists to ensure the well-being of local flora and fauna, implementing measures to protect and manage wildlife during construction.

To date, Seqwater and John Holland have undertaken extensive environmental investigations to identify and record plant and animal habitats in and around Lake Macdonald. 

The investigations include field surveys focusing on protected plants, important habitats for plants and animals, aquatic environments and significant local species. It also included reviewing past and present reports and databases. 

Click here for more information on ecological management and mitigation measures.

Investigations are underway into the measures needed to manage aquatic fauna at the 42% or 93m reduced water level. Seqwater will develop a recovery and relocation plan, in consultation with key stakeholders, to manage any aquatic fauna impacted during the lowering and throughout construction. 

It is expected there will be a period when the habitat available for aquatic species, including those of conservation significance such as the Mary River cod, Australian lungfish, Mary River turtle, white-throated snapping turtle, and platypus, is limited. To minimise the impacts to these important species, Seqwater is proposing an initial aquatic fauna relocation program.  

We will aim to relocate species of conservation significance before construction begins. Some fish are sensitive to handling or changes in water temperature and may suffer injury or mortality if relocated. Therefore, appropriate measures will need to be identified and incorporated into the management approach. 

All relocation will be delivered by expert fish biologists, via a purpose-built fish transport vehicle to Cooloolabin Dam.

There is no existing fish passage (a fish ladder is a specific type of fish passage) at Lake Macdonald Dam, and no proposed fish passage included in the Lake Macdonald Dam Improvement Project. The reasons for this are:   

•  A fish passage could allow for pest species such as Tilapia to enter Lake Macdonald reservoir.  
• A more suitable location for a fish passage has been identified at the Gympie Weir. A fish passage in this location will allow fish to pass up and down the main Mary River, allowing passage between the upper tributaries and reaches.
• The Coordinator-General, as part of the Project Approval Conditions, has stated that Seqwater upgrade the Gympie Weir to include a fish passage.