The toxic sludge filling Lake Burley Griffin has cleared markedly over the past week, the National Capital Authority says, but still poses a danger to swimmers and boaters.
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The authority closed the entire lake last week, saying any primary contact with the water would be dangerous.
The lake remains closed to swimming or any activity involving head submersion, with blue-green algae levels dropping to 250,000 per milliltre this week.
"The worst affected areas last week recorded a count of 66 million cells per millilitre, compared to a rate of 250,000 per milliltre this week," authority chief executive Gary Rake said today.
"This is still five times higher than the levels considered safe for activities such as swimming."
He said swimmers, inexperienced boaters or people using unstable boat craft should avoid using the lake until the water improved.
So-called "secondary contact recreation", such as rowing, fishing, boating and canoeing will still be permitted.
The authority said blue-green algae exposure symptoms included flu-like symptoms, gastro-intestinal problems, and eye, ear, throat, nose and mouth irritation.
Anyone who comes into contact with the water should shower after contact.
The Captain Cook Memorial Jet in Central Basin will remain turned off, to avoid winds creating fine mists and sending algae across the lake surface.
Pet owners should not allow their animals to swim in or drink lake water.
For further information on the lake's water quality, visit the NCA website.
