What's up with Woods Lake?

Located in the Central Highlands, Woods Lake plays an important role in generating energy for Tasmanians, as well as providing valuable irrigation water to downstream users. Woods Lake is also renowned for its trout fishing.

There has been an ongoing blue-green algae (cyanobacteria) bloom at Woods Lake since February 2023. This bloom is non-toxic and fishing is allowed. Read below for more information on the bloom, what we're doing about it and advice for recreational use of the lake.


Woods Lake bloom - Winter 2024 Update

The bloom is continuing to persist in the lake despite measures taken to dilute the concentration of algal cells and, instead, promote aquatic plant growth. We expect that blue-green algae may continue to be present at Woods Lake for some time to come.

  • The blue-green algae population continues to persist into July.
  • Cell numbers may decline as a result of recent inflows providing dilution combined with sustained low temperatures.
  • We expect the population may reduce and then re-emerge in summer as occurred from December 2023.
  • Whilst the bloom may reduce in concentration and become less dominant, it is expected that when environmental conditions are optimal the residual population will again go through a rapid growth phase, as seen in the graph below over the last couple of years.



This chart represents the concentration of the current dominant bloom species (Dolichospermum sp.) collected from water samples from woods lake and analysed in the lab. The species has dominated the ecosystem since cells numbers grew rapidly from late February 2023.




Releases into the Lake River from Woods Lake have ceased over the winter period so will see a natural rise in the water level with local catchment inflows.

Fishing is permitted in the lake, but entrails should be disposed of and not left for wildlife.





Blue-green algae (cyanobacteria) bloom at Woods Lake.

Check out the widget on the right hand-side for more information on what blue-green algae is.

What caused this recent blue-green algae bloom?

At Woods Lake, consecutive years of La Nina may have contributed to a larger amount of naturally occurring nutrients flowing into the catchment and lake. However, there are also a range of other possible contributing factors that we are investigating with an expert scientific panel.


What does this mean for you?

While the bloom is non-toxic, direct contact or consumption of blue-green algae can pose a health risk.


People are advised not to enter the water and to avoid exposure to water spray if boating on the lake.


If you do have significant contact with the water, wash yourself down with clean water to remove any algae. Wash all clothing and equipment with clean water.


Any fish caught can be consumed but should be washed in clean water, gilled, gutted and all internal organs disposed of. Care should be taken that animals are not fed or allowed to eat the entrails of these fish. This is a precautionary measure as if there happened to be any toxins present, they can accumulate within the internal organs of fish and cause animals to become ill.


Good practice is to clean all equipment between lakes, including washing down boats, to do our collective best to prevent the spread of blue green algae.



What we are doing about it

We’ve been working closely with a range of external experts including representatives from the University of Western Australia (UWA), Griffith University and the University of Tasmania to investigate the drivers of the bloom and provide guidance around potential mitigation or management measures.

Based on this expert advice, we have previously drawn down water levels in an attempt to dilute concentrations of cyanobacteria (blue-green algae) and to encourage the growth of aquatic plants by enabling sunlight to reach the sediment.

Our expert panel has found the strain of blue-green algae isolated from Woods Lake has an optimal temperature of 25°C where maximum growth occurs, but also has an unusually high tolerance to low temperatures.

We’re hoping in time, management measures will help shift the lake from a blue-green algae dominated and murky system to the clear, plant dominated system you’re used to.

We’re also working with our colleagues at UWA to develop scientific models to assist with early identification of blooms in future and how best to manage future scenarios using available levers at our disposal.

Our current monitoring program consists of a combination of fortnightly manually collected water samples for analysis in the lab and a permanent water quality raft that collects and transmits data every 15 minutes.

Water quality parameters monitored include:

  • Nutrients including dissolved nutrients.
  • Water temperature
  • Turbidity (clarity)
  • pH
  • Dissolved oxygen
  • Electrical conductivity
  • Algae and blue-green algae cell counts / identification
  • Suspended solids
  • Organic carbon


Located in the Central Highlands, Woods Lake plays an important role in generating energy for Tasmanians, as well as providing valuable irrigation water to downstream users. Woods Lake is also renowned for its trout fishing.

There has been an ongoing blue-green algae (cyanobacteria) bloom at Woods Lake since February 2023. This bloom is non-toxic and fishing is allowed. Read below for more information on the bloom, what we're doing about it and advice for recreational use of the lake.


Woods Lake bloom - Winter 2024 Update

The bloom is continuing to persist in the lake despite measures taken to dilute the concentration of algal cells and, instead, promote aquatic plant growth. We expect that blue-green algae may continue to be present at Woods Lake for some time to come.

  • The blue-green algae population continues to persist into July.
  • Cell numbers may decline as a result of recent inflows providing dilution combined with sustained low temperatures.
  • We expect the population may reduce and then re-emerge in summer as occurred from December 2023.
  • Whilst the bloom may reduce in concentration and become less dominant, it is expected that when environmental conditions are optimal the residual population will again go through a rapid growth phase, as seen in the graph below over the last couple of years.



This chart represents the concentration of the current dominant bloom species (Dolichospermum sp.) collected from water samples from woods lake and analysed in the lab. The species has dominated the ecosystem since cells numbers grew rapidly from late February 2023.




Releases into the Lake River from Woods Lake have ceased over the winter period so will see a natural rise in the water level with local catchment inflows.

Fishing is permitted in the lake, but entrails should be disposed of and not left for wildlife.





Blue-green algae (cyanobacteria) bloom at Woods Lake.

Check out the widget on the right hand-side for more information on what blue-green algae is.

What caused this recent blue-green algae bloom?

At Woods Lake, consecutive years of La Nina may have contributed to a larger amount of naturally occurring nutrients flowing into the catchment and lake. However, there are also a range of other possible contributing factors that we are investigating with an expert scientific panel.


What does this mean for you?

While the bloom is non-toxic, direct contact or consumption of blue-green algae can pose a health risk.


People are advised not to enter the water and to avoid exposure to water spray if boating on the lake.


If you do have significant contact with the water, wash yourself down with clean water to remove any algae. Wash all clothing and equipment with clean water.


Any fish caught can be consumed but should be washed in clean water, gilled, gutted and all internal organs disposed of. Care should be taken that animals are not fed or allowed to eat the entrails of these fish. This is a precautionary measure as if there happened to be any toxins present, they can accumulate within the internal organs of fish and cause animals to become ill.


Good practice is to clean all equipment between lakes, including washing down boats, to do our collective best to prevent the spread of blue green algae.



What we are doing about it

We’ve been working closely with a range of external experts including representatives from the University of Western Australia (UWA), Griffith University and the University of Tasmania to investigate the drivers of the bloom and provide guidance around potential mitigation or management measures.

Based on this expert advice, we have previously drawn down water levels in an attempt to dilute concentrations of cyanobacteria (blue-green algae) and to encourage the growth of aquatic plants by enabling sunlight to reach the sediment.

Our expert panel has found the strain of blue-green algae isolated from Woods Lake has an optimal temperature of 25°C where maximum growth occurs, but also has an unusually high tolerance to low temperatures.

We’re hoping in time, management measures will help shift the lake from a blue-green algae dominated and murky system to the clear, plant dominated system you’re used to.

We’re also working with our colleagues at UWA to develop scientific models to assist with early identification of blooms in future and how best to manage future scenarios using available levers at our disposal.

Our current monitoring program consists of a combination of fortnightly manually collected water samples for analysis in the lab and a permanent water quality raft that collects and transmits data every 15 minutes.

Water quality parameters monitored include:

  • Nutrients including dissolved nutrients.
  • Water temperature
  • Turbidity (clarity)
  • pH
  • Dissolved oxygen
  • Electrical conductivity
  • Algae and blue-green algae cell counts / identification
  • Suspended solids
  • Organic carbon


What's on your mind 🗣

loader image
Forgot password?
Didn't receive confirmation?
Seems like you are already registered, please provide the password. Forgot your password? Create a new one now.

  • Hello - What impact is the outbreak having on the fish population? Would we expect to get some good fish in numbers if we went there in October this year?

    Drew Mc asked 19 days ago

    Hi Drew, 

    Thanks very much for your question. Our Environment Team tell me that the Inland Fisheries Service (IFS) are currently planning a fishery performance assessment for Woods Lake. IFS are responsible for fisheries management and will be able to give us the best information on the status of the population. So I can't give you any more detail at the moment; however, some should be available in the near term. 

  • Is this bloom over the last few years responsible or partly responsible for the drastic decline in the coot and swan populations at Woods? Is there any evidence that insect larval populations are also affected and that possible trout organ toxicity could be due their food? It is particularly concerning if blue-green algae and potential toxins are biomagnified in trout food chains. Should not the levels of cyanotoxins be monitored in trout organs to determine if trout populations are indeed affected?

    Mike Fishburn asked about 1 month ago

    Hi Mike, Great question. We've been working closely with CSIRO scientists to determine the genetics of the blue green algae species at Woods Lake. We have confirmed the population does not have any toxin producing genes and therefore organ toxicity or biomagnification of toxins from the algal bloom are not possible. Given the lack of toxicity, we do not believe that impacts to insect or bird populations would occur as a result of the bloom. 

  • How long after catching a fish, before it can be gutted.

    Glenn Ernest asked about 1 month ago

    Hi Glenn, Thanks very much for checking in and asking a question. You can gut any trout you catch as soon as you wish. We just ask that you dispose of the entrails responsibly to keep the onshore area pleasant for all visitors.  

  • Hi, I just have one question/concern regarding the algae issue at Woods Lake. One of the directions under the heading "What does this mean for you" states 'Wash all clothing and equipment with clean water'. I was home for Christmas this/last year, and fished Woods Lake for one day. On that particular day we saw multiple boats on the water, and these boats departed the lake just prior to us. We returned to our home at the Great Lake, whereby, I quickly hosed down our car/boat & trailer, along with rinsing the fishing gear we used, etc. However, while I was doing this task I observed (from our home which stops at the lakes edge) a couple of the boats that departed Woods Lake just before us were out & already trolling on the water at the Great Lake by the time we got home (ie, there would not have been enough time for them to clean their gear & then enter the Great Lake, etc). So my concern is, can the Woods Lake algae be transferred between lakes (via dirty/unclean boats/trailers), and if so, what contingencies do you currently have in place to monitor/ensure that the algae won't end up in other lakes, etc

    mark asked about 2 months ago

    Hi Mark,

    Thanks for your question. Firstly, we really appreciate and encourage your efforts in rinsing down all your equipment. This a prudent precautionary measure and good practice in reducing the spread of invasive aquatic vegetation. 

    Regarding the spread of blue-green algae, it is very unlikely that the transfer of cells would result in a bloom in yingina / Great Lake as many environmental factors have to come together for a bloom to occur. 

    Our environmental teams at Hydro Tasmania conduct surveillance for algal blooms routinely across our lakes which helps to detect any indication of blue-green algae growth in other storages and systems. Particularly, the use of satellite imagery is beneficial for this monitoring practice. This means that if, on the very low chance that blue green algae was transferred to yingina / Great Lake, our team would know about it swiftly and be able to act accordingly.

    Thanks again for your question and thank you for your efforts in reducing the spread of invasive organisms between our water systems. 


  • Hi, what species of blue green algae is found in Woods Lake Thanks

    Joe asked about 2 months ago

    Hi Joe, Thanks for your question. We’ve been working with scientists at CSIRO to determine the genetics of the blue green algae so that we understand how it is likely to behave in response to temperature and other environmental factors. We know that the blue green algae at Woods Lake is of the genus Dolichospermum. We haven't yet confirmed what the species is; however, for management purposes we would treat all Dolichospermum sp. the same way. Importantly, tests indicate the current population contains no toxin producing genes.