It's the latest outbreak despite millions of dollars being spent to prevent such incidents which are now occurring annually.

The ACT government warns that touching the stuff "carries an increased health risk". Symptoms of exposure could be skin irritation, flu-like symptoms and "gastrointestinal illness".

Pet owners are warned that animals may die if they come into contact with it.

The government has closed the lake to recreation which involves contact with the water, recreations like swimming, diving, water-skiing or windsurfing.

Other recreations which don't need such close contact - like rowing, fishing, boating and canoeing - are still allowed.

But health officials warn that people should avoid these "secondary-contact" recreations unless they know what to do if they get some of the algae on their skin.

They should also be able to shower quickly after coming into contact with the algae.

The health officials are particularly worried about "algal scum".

"Individuals should avoid contact with algal scum. Any clothing that has been in the water should be washed to remove blue-green algae residue."

Organisers of events on or near the water should make sure participants are aware of the risks and of what to do if they come into contact with the algae.

Animals should also be kept away from the water.

"Pet owners should not allow their animals to swim in or drink the water, as blue-green algae can make pets very ill or even result in death," a statement said.

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This closure of the created lake is the latest in what is becoming a regular headache for health officials and the public.

It's estimated that more than $30 million has been spent by governments and environmental groups to clear the algae.

The most recent initiative involved the launch of floating wetlands, designed to absorb many of the nutrients that form the algal blooms.

With the latest outbreak, people are urged to look for warning signs.

"Algae levels can change quickly. Water users should look for algae warnings signs which indicate the current algae alert level. Warning signs are located at public access areas.

"Anyone concerned about possible symptoms of blue-green algae exposure following water exposure should contact their GP."

Algae has been so thick on Lake Burley Griffin in the past that it can be seen from space.

The European Space Agency's Copernicus Sentinel-2 satellite picked up masses of the blue-green stuff as it passed over south-eastern Australia.

Algae in profusion is usually caused in the summer as temperatures rise.

Still waters, like Lake Tuggeranong and Lake Burley Griffin, are ideal conditions as sunlight works chemically on organisms in the warm water.

"Still water that isn't 'mixed' by winds, rain, regular or high flows provides ideal conditions for algae to grow," according to the ACT government.

"Thermal stratification (when the water in the lake forms layers) means the cooler bottom layer becomes anoxic (without oxygen), causing nutrients to be released from the sediment which feed the algae."

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