Lake Hamilton – Action plan for the improvement of water quality

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The Southern Grampians Shire Council (SGSC) engaged GHD to develop an Action Plan to improve water quality in Lake Hamilton in Australia. The overall aim of the Action Plan was to manage and prevent high levels of Cyanobacteria (blue-green algae) and Escherichia coli (E. coli).


Lake Hamilton is located in western Victorian, Australia and is fed by the Grange Burn, urban stormwater and overland flow. Recurring high levels of Cyanobacteria and E. coli has resulted in the SGSC erecting warning signs to deter the use of the lake due to potential public health issues.

The most significant finding of the Action Plan was that Lake Hamilton has undergone a long period of eutrophication. The main factor contributing to Cyanobacterial blooms was excessive nutrients entering the lake from stormwater and the Grange Burn. There is also a large bank of nutrients contained within the lake sediments.

Short to medium-term management actions include the use of chemicals (as algicides), microorganisms to consume nutrients, and dyes to attenuate sunlight and discourage algal growth. However, these options may pose risks to the lake and further downstream in the Grange Burn. There is also a large financial cost associated with their use.

Artificial aeration was another potential short to medium-term action aimed at breaking down water column stability (stratification which promotes algal growth) and creating oxygenated conditions in the water column to limit the release of nutrients from the sediment. Currently, there is no evidence of seasonal stratification so this action can only be considered following a more comprehensive investigation.

Dredging of the lake sediments was considered to reduce the pool of nutrients. The large financial costs associated with dredging and the impacts on the Lake ecosystem resulted in this action not being recommended. 

Ultimately, Lake Hamilton requires long-term management actions to address the problem of eutrophication. Such actions should be aimed at reducing nutrient inputs from the Grange Burn. Significant catchment management, such as the introduction of riparian buffer strips, stabilisation of riparian zones and improved farming practices are required to limit nutrient entry and further eutrophication. Maintenance and enhancement of macrophytes was identified as an important action as they have the capacity to reduce nutrients. Reduction of nutrients could also be achieved by construction of a treatment wetland upstream of the Lake and by introducing stormwater treatment swales.

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